last updated Mon, Apr 1, 2002

Infrared Spectroscopy Dr.A.Bacher

V ibrational modes within a molecule can be described using the anharmonic oscillator model. This model assumes that the two masses (with known weight) are connected with a spring (with known strength). With the help of quantum mechanical calculations (Schroedinger equation) you can find the frequencies of basic stretching and bending modes:

ir peaks at 2200

From this equation, one can deduce some basic trends can be deducted: a. If the force constant F (= bond strength) increases, the stretching frequency will increase as well (in cm -1 )

b. If the masses of the involved atoms increase, the peak will shift to lower wavenumbers e.g. H/D-exchange in labeling experiments although the bond strength remains the same.

Based on the equation, one would always expect a sharp lines at a well defined wavenumber. Unfortunately, the change in vibration modes is always accompanied with change in rotational mode (Stokes and Anti-Stokes). The required energy for this process is much smaller (1-5 cm -1 ) and causes together with some other effects the broading of the 'lines'. The number of basic stretching and bending modes expected for a molecule increases with the number of atoms in the molecule. For non-linear molecules 3N-6 (2N-5 bending, N-1 stretching) vibrations are observed (e.g. CH 2 Cl 2 ). For linear molecules e.g. CO 2 one expect to find 3N-5 (3*3-5=4) modes. If there is no symmetry in the molecule most of them will be observed the IR spectrum; the remaining modes will be observed in a Raman spectrum. The more complicated the molecule is (the more atoms it possesses and the lower the symmetry), the more peaks can be observed in the IR spectrum (see example 3 and 4 ). A signal is only observed in the IR spectrum, if the dipole momentum of the molecule changes during the interaction with the electromagnetic radiation. This is very likely for groups which already possess a significant dipole momentum to start with e.g. C-O, C-Cl, O-H, etc. (strong peaks). Groups with a small difference in electronegativity e.g. C-H, C-C, C=C, etc., will usually show weak or medium sized peaks in the IR spectrum. An interpretation of an IR spectrum should include a detailed assignment of the peaks: exact wavenumber from the spectrum (integer), the intensity (w/m/s/br) and which functional group it represents, and maybe in addition the corresponding literature value. However, it is not necessary to interpret every little peak in the IR spectrum. Also, be cautious when you compare spectra which were obtain with different techniques (solution, Nujol mull, KBr pellet). The actual number of your vibration changes quite at bit, especially for highly polar compounds (Why ?). 2. Interpretation of the spectrum The IR-spectrum can be divided into five ranges major ranges of interest for an organic chemist: a. From 2700-4000 cm -1 (E-H-stretching: E=B, C, N, O) In this range typically E-H-stretching modes are observed. The C-H-stretching modes can be found between 2850 and 3300 cm -1 , depending on the hydrization . The range from 2850-3000 cm -1 belongs to saturated systems (alkanes, sp 3 , example 1 ), while the peaks from 3000-3100 cm -1 indicate an unsaturated system (alkenes, sp 2 , example 2; aromatic ring, example 3,4 ). Latter ones are usually weak or medium in intensity. The CH-function on a C-C-triple bond (alkynes) will appear as a sharp, strong peak around 3300 cm -1 . The differences in wavenumbers are mainly due to different hybridization (=bond strength, the s-character in the bond, the stronger the bond is) and number of ligands on the carbon atom. The O-H-stretching modes from alcohols and phenols ( example 5 ) are mostly broad and very strong (3200-3650 cm -1 ) The O-H-peaks due to carboxylic acids ( example 6 ) show a very broad and less intense peak between 2500 and 3500 cm -1 . The change in peak shape is a result of the different degree of hydrogen bonds in alcohol and carboxylic acids. These peaks change significantly with the polarity of the solvent. They usually become sharper if the polarity of the solvent increases e.g. camphor in CCl 4 and CH 2 Cl 2 (see reader). P eaks that are due to N-H-stretching modes are sharper than O-H-peaks (3300-3500 cm -1 ). Primary amines ( example 7 ) have two peaks (sym./asym. vibration) in this range, while secondary amines ( example 8 ) have only one peak. There are no peaks in this area for tertiary amines. Why?

ir peaks at 2200

Two small or medium peaks at ~2750 and ~2850 cm -1 are a result of an aldehyde ( example 15 ). b. From 2000 - 2700 cm -1 (E-X-triple bonds: E=X=C, N, O) This range covers mainly the triple bond stretching modes. The C-C-triple bond of alkynes (2130-2150 cm -1 ) is usually fairly weak, if observed at all. The C-N-triple bond of nitriles ( example 10 ) (2100-2160 cm -1 ). In most cases a peak (with varying intensity) around 2349 cm -1 (together with 667 cm -1 ). This is due to the CO 2 in the beam (poor background correction). c. From 1500 - 2000 cm -1 (E-X-double bonds: E=X=C, N, O) This is the most important range in the entire IR spectrum for organic chemists. If there is a very strong peak between 1640 and 1850 cm -1 , there is most likely a carbonyl function in the molecule. Analysis of the exact peak position will reveal further what type of carbonyl function is present. The general rule is the more reactive the carbonyl compound is, the further to the right (=higher wavenumber) the C=O stretching frequency will be. The following sequence is observed:

acid chlorides > anhydrides > ester > aldehydes > ketones > carboxylic acids > amides

In order to identify a specific group additional information is needed from the other ranges of the IR spectrum:

Ring strain usually increases the C=O stretching frequency. Conjugation of teh carbonyl group with other double bonds (aromatics, alkenes) or the formation of hydrogen bonds decreases the bond strength (shift: 15-60 cm -1 to lower wavenumbers) as the following examples of cyclic ketones demonstrate.

ir peaks at 2200

For all 'anhydride type systems' (O=C-X-C=O, X=O, NR, S, CH 2 ) two peaks are observed in this region due to a symmetric and an asymmetric stretching mode.

ir peaks at 2200

In addition to the dominant C=O-mode, the C-C-double bond ( example 2 -4 )is also located in this area (1600-1660 cm -1 ). However, if there is a carbonyl group present, it might be difficult to locate a weak or medium sized peak right next to it. Sometimes it is only observed as a shoulder. If there is a coupling between a C=C-group and other double bonded systems e.g. C=O or aromatic systems, the intensity will increase due to the increase in dipole momentum in the double bond. A medium or strong peak in this area corresponds to aromatic ring. A nitro group shows two very intense peaks in the range between 1300-1400 cm -1 (sym.) and 1500-1600 cm -1 (asym.) ( example 17 ).In a good spectrum, it might be possible to deduct the substitution pattern on an aromatic system from the overtone combination vibrations in the range from 1660-2000 cm -1 e.g. four peaks with increasing intensity are characteristic for a monosubstitution on your ring ( example 4 and table for Arenes below). d. From 1000-1500 cm -1 (E-X-single bonds, deformation, rocking modes) A strong peak around 1450 cm -1 indicates the presence of methylene groups (CH 2 ), while an additional strong peak about 1375 cm -1 is caused by a methyl group (CH 3 ) ( examples 1, 8-10 ). A symmetric 'doublet' with medium intensity around 1370 cm -1 is characteristic for an isopropyl group, while an asymmetric 'doublet' between 1365 and 1390 cm -1 is often due to a t-Bu-group. The C-O-C-functions of ethers and esters are typically found as strong peaks in the range between 1000 and 1300 cm -1 ( example 13 ). Generally, assignments in this area have to be done with extreme care, because there are a lot of ring absorbances in this ‘ fingerprint area ’. e. Below 1000 cm -1 (out of plane modes, C-X: X=Cl, Br, I, heavier atoms) This range belongs to the ’fingerprint area’, where assignments are a little bit uncertain. In some cases you can find information about the substitution pattern of alkenes or aromatic ring systems, if the range between 700-900 cm -1 is analyzed correctly (oop bending).

4. Examples Example 1 : Alkane - Undecane

Home / Infrared Spectroscopy: A Quick Primer On Interpreting Spectra


By James Ashenhurst

  • Infrared Spectroscopy: A Quick Primer On Interpreting Spectra

Last updated: October 31st, 2022 |

How To Interpret IR Spectra In 1 Minute Or Less: The 2 Most Important Things To Look For [Tongue and Sword]

Last post , we briefly introduced the concept of bond vibrations, and we saw that we can think of covalent bonds as a bit like balls and springs:  the springs vibrate, and each one “sings” at a characteristic frequency, which depends on the strength of the bond and on the masses of the atoms.  These vibrations have frequencies that are in the mid-infrared (IR) region of the electromagnetic spectrum.

We can observe and measure this “singing” of bonds by applying IR radiation to a sample and measuring the frequencies at which the radiation is absorbed. The result is a technique known as Infrared Spectroscopy , which is a useful and quick tool for identifying the bonds present in a given molecule.

We saw that the IR spectrum of water was pretty simple – but moving on to a relatively complex molecule like glucose (below) we were suddenly confronted with a forest of peaks!

ir spectrum of glucose how do we analyze this with so many peaks dont panic

Your first impression of looking at that IR might be: agh!  how am I supposed to make sense of that??

To which I want to say:  don’t panic! 

Table of Contents

  • Let’s Correct Some Common Misconceptions About IR
  • Starting With “Hunt And Peck” Is Not The Way To Go
  • IR Spectroscopy: The Big Picture
  • The Two Main Things To Look For In An IR Spectrum: “Tongues” and “Swords”.
  • Alcohols and Carboxylic Acids: More Detail
  • Specific Examples of IR Spectra of Carbonyl Functional Groups
  • Less Crucial, But Still Useful: Two More Very Diagnostic Areas.
  • Glucose, Revisited: The 1 Minute Analysis

1. Let’s Correct Some Common Misconceptions About IR

In this post, I want to show that a typical analysis of an IR spectrum is much simpler than you might think. In fact, once you learn what to look for, it can often be done in a minute or less.  Why?

  • IR is not generally used to determine the whole structure of an unknown molecule. For example, there isn’t a person alive who could look at the IR spectrum above and deduce the structure of glucose from it. IR is a tool with a very specific use. [Back in 1945 when IR was one of the few spectral techniques available, it was necessary to spend a lot more time trying to squeeze every last bit of information out of the spectrum. Today, with access to NMR and other techniques, we can do more cherry-picking]
  • We don’t need to analyze every single peak  ! (as we’ll see later, that’s what NMR is for : – )  ).   Instead, IR is great for  identifying certain specific functional groups , like alcohols and carbonyls. In this way it’s complimentary to other techniques (like NMR) which don’t yield this information as quickly.

With this in mind, we can simplify the analysis of an IR spectrum by cutting out everything except the lowest-lying fruit. 

See that forest of peaks from 500-1400 cm -1 ? We’re basically going to ignore them all!

80% of the most useful information for our purposes can be obtained by looking at  two specific areas of the spectrum : 3200-3400 cm -1 and 1650-1800 cm -1 . We’ll also see that there are at least two more regions of an IR spectrum worth glancing at, and thus conclude a “first-order” analysis of the IR spectrum of an unknown. [We might write a subsequent post which gets nittier and grittier about the finer points of analyzing an IR spectrum]

Bottom line: The purpose of this post is to show you how to  prioritize your time  in an analysis of an IR spectrum.

[BTW: all spectra are from the NIST database . Thank you, American taxpayers!]

2. Starting With “Hunt And Peck” Is Not The Way To Go

Confronted with an IR spectrum of an unknown (and a sense of rising panic), what does a typical new student do?

They often reach for the first tool they are given, which is a table of common ranges for IR peaks given to them by their instructor.

The next step in their analysis is to go through the spectrum from one side to the next, trying to match every single peak to one of the numbers in the table. I know this because this is exactly what I did when I first learned IR.  I call it “hunting and pecking”.

for gods sake when interpreting ir spectra dont hunt and peck with a table instead know what to look for

The only people who “hunt and peck” as their first step are people who have no plan  (i.e. “newbies”).

So by reading the next few paragraphs you can save yourself a lot of time and confusion.

[Hunt and peck has its place, but only AFTER  you’ve looked for “tongues” and “swords”, below. Hunting and pecking is great to make sure you didn’t miss anything big – but as a first step, it’s bloody awful!]

3. The Big Picture

In IR spectroscopy we measure where molecules absorb photons of IR radiation. The peaks represent areas of the spectrum where specific bond vibrations occur. [for more background, see the previous post, especially on the “ball and spring” model] . Just like springs of varying weights vibrate at characteristic frequencies depending on mass and tension, so do bonds.

Here’s an overview of the IR window from 4000 cm  -1  to 500 cm  -1  with various regions of interest highlighted.

An even more compressed overview looks like this: ( source )

Within these ranges, there are  two high-priority areas to focus on , and two lesser-priority areas we’ll discuss further below.

4. The Two Main Things To Look For In An IR Spectrum: “Tongues” and “Swords”.

When confronted with a new IR spectrum, prioritize your time by asking two important questions:

  • Is there a broad, rounded peak in the region around 3400-3200 cm -1 ? That’s where hydroxyl groups ( OH ) appear.
  • Is there a sharp, strong peak in the region around 1850-1630 cm -1 ? That’s where carbonyl groups ( C=O ) show up.

First, let’s look at some examples of hydroxyl group peaks in the 3400 cm -1 to  3200 cm -1  region,  which Jon describes vividly as “tongues”. The peaks below all belong to alcohols. Hydrogen bonding between hydroxyl groups leads to some variations in O-H bond strength, which results in a range of vibrational energies. The variation results in the broad peaks observed.

Hydroxyl groups that are a part of carboxylic acids have an even broader appearance that we’ll describe in a bit.

collection of o h stretches for alcohols 5 examples

[Sometimes it helps to know what not to look for. On the far right hand side is included one example of a very weak peak on a baseline that you can safely ignore.]

The main point is that  a hydroxyl group isn’t generally something you need to go looking for in the baseline noise.

Although hydroxyl groups are the most common type of broad peak in this region, N-H peaks can show up in this area as well (more on them in the Note 1 ). They tend to have a sharper appearance and may appear as one or two peaks depending on the number of N-H bonds.

Next,  let’s look at some examples of   C=O peaks, in the region around 1630-1800 cm -1. . These peaks are almost always the strongest peaks in the entire spectrum and are relatively narrow, giving them a somewhat “sword-like” appearance.

collection of c o stretches around 1700 for aldehydes ketones esters carboxylic acids

That sums up our 80/20 analysis: look for tongues and swords.

If you learn nothing else from this post, learn to recognize these two types of peaks!

Two other regions of the IR spectrum can quickly yield useful information if you train yourself to look for them.

3. The line at 3000 cm -1 is a useful “border” between alk ene  C–H (above 3000 cm -1 )   and alk ane C–H (below 3000 cm -1  ) This can quickly help you determine if double bonds are present.

4. A peak in the region around 2200 cm -1 – 2050 cm -1  is a subtle indicator of the presence of a triple bond [C≡N or C≡C] . Nothing else shows up in this region.

A Common Sense Reminder

First, some obvious advice:

  • if you’re given the molecular formula, that will determine what functional groups you should look for. It makes no sense to look for OH groups if you have no oxygens in your molecular formula, or likewise the presence of an amine if the formula lacks nitrogen.
  • Less obviously,  calculate the degrees of unsaturation   if you are given the molecular formula, because it will provide important clues. Don’t look for C=O in a structure like C 4 H 10 O which doesn’t have any degrees of unsaturation.

5. Alcohols and Carboxylic Acids: More Detail

Let’s look at a specific example so we can see everything in perspective. The spectrum below is of 1-hexanol.

Note the hydroxyl group peak around 3300 cm -1  , typical of an alcohol   (That sharp peak around 3600 cm -1  is a common companion to hydroxyl peaks: it represents non-hydrogen bonded O-H). 

ir spectrum of hexanol

To gain some familiarity with variation,  here’s some more examples of entire IR spectra of various alcohols.

  • Cyclohexanol 

Carboxylic Acids

Hydroxyl groups in carboxylic acids are considerably broader than in alcohols. Jon calls it a “hairy beard”, which is a perfect description. Their appearance is also highly variable. The OH absorption in carboxylic acids can be so broad that it extends below 3000 cm -1 , pretty much “taking over”  the left hand part of the spectrum.

Here’s an example: butanoic acid.

ir spectrum of butanoic acid

Here’s some more examples of full spectra so you can see the variation.

  • Benzoic acid ,
  • Pentanoic acid ,
  • Acetic acid

The difference in appearance between the OH of an alcohol and that of a carboxylic acid is usually diagnostic. In the rare case where you aren’t sure whether the broad peak is due to the OH of an alcohol or a carboxylic acid, one suggestion is to check the region around 1700 cm for the C=O stretch. If it’s absent, you are likely looking at an alcohol.

[ Note 1 for more detail on the 3200-3500 cm -1 region : Amines, Amides, and Terminal Alkynes]

6. Specific Examples of IR Spectra of Carbonyl Functional Groups

The second important peak region is the carbonyl C=O stretch area at about 1630-1830 cm. Carbonyl stretches are sharp and strong.

Once you see a few of them they’re impossible to miss. Nothing else shows up in this region.

To put it in perspective, here’s the IR spectrum of hexanal. That peak a little after 1700 cm -1 is the C=O stretch.  When it’s present, the C=O stretch is almost always the strongest peak in the IR spectrum and impossible to miss.

ir spectrum of hexanal

The position of the C=O stretch varies slightly by carbonyl functional group. Some ranges (in cm -1 ) are shown below:

  • Aldehydes (1740-1690): benzaldehyde , propanal , pentanal
  • Ketones (1750-1680): 2-pentanone , acetophenone
  • Esters (1750-1735): ethyl acetate , methyl benzoate
  • Carboxylic acids (1780-1710): benzoic acid , butanoic acid
  • Amide (1690-1630): acetamide , benzamide ,  N,N -dimethyl formamide (DMF)
  • Anhydrides (2 peaks; 1830-1800 and 1775-1740): acetic anhydride , benzoic anhydride

Conjugation will affect the position of the C=O stretch somewhat, moving it to lower wavenumber.

A decent rule of thumb is that you will never, ever see a C=O stretch below 1630. If you see a strong peak at 1500, for example, it is  not C=O. It is something else.

7. Less Crucial, But Still Useful: Two More Very Diagnostic Areas.

  • The C-H Stretch Boundary at 3000 cm -1

3000 cm -1 serves as a useful dividing line. Above this line is observed higher frequency C-H stretches we attribute to sp 2 hybridized C-H bonds. Two examples below: 1-hexene (note the peak that stands a little higher) and benzene.

For a molecule with only sp 3 -hybrized C-H bonds, the lines will appear below 3000 cm -1 as in hexane, below.

the dividing line at 3000 cm 1 between sp3 ch bonds and sp2 c h bonds

2. The Distinctive Triple Bond Region around 2200 cm -1

Molecules with triple bonds appear relatively infrequently in the grand scheme of things, but when they do, they do have a distinctive trace in the IR.

The region between 2000 cm -1 and 2400 cm -1   is a bit of a “ghost town” in IR spectra; there’s very little that appears in this region. If you do see peaks in this region, a likely candidate is a triple bonded carbon such as an alkyne or nitrile .

triple bonds have distinctive stretch around 2050 to 2250 nitriles alkynes

Note how weak the alkyne peaks are.  This is one exception to the rule that one should ignore weak peaks. Still, caution is required: if you’re given the molecular formula, confirm that an alkyne is possible by calculating the degrees of unsaturation and ensuring that it is at least 2 or more.

Terminal alkynes (such as 1-hexyne) also have a strong C-H stretch around 3400 cm -1  that is more strongly diagnostic.

8. Glucose, Revisited: The 1 Minute Analysis

OK. We’ve gone over 4 regions that are useful for a quick analysis of an IR spectrum.

  • (important!) O-H around 3200-3400 cm -1
  • (important!) C=O around 1700 cm -1
  • C-H dividing line at 3000 cm -1
  • (rare) Triple bond region around 2050-2250 cm -1

Now let’s go back and look at the IR of glucose. What do we see?

1 minute analysis of ir of glucose has oh no alkene ch no c o double bond

Here are the two big things to note:

  • OH present around 3300 cm -1  . (in fact, this was included as one of the “swords” in section #3,  above)
  • No C=O stretch present. No strong peak around 1700 cm -1   . (The peak at 1450 cm -1   isn’t a C=O stretch).

Also, if we take a bit of extra time we can see:

  • No alkene C-H (no peaks above 3000 cm -1  )
  • Nothing in triple bonded region (rare, but still an easy thing to learn to check)

Now: If you were given this spectrum as an “unknown” along with its molecular formula, C 6 H 12 O 6 , what conclusions could you draw about its structure?

  • The molecule has at least one OH group (and possibly more)
  • The molecule doesn’t have any C=O groups
  • The molecule *likely* doesn’t have any alkenes. If any alkenes are present, they don’t bear any C-H bonds, because we’d see their C-H stretch above 3000 cm -1 .

A molecule with one degree of hydrogen deficiency (C 6 H 12 O 6 ) but no C=O, and likely no C=C ?

A good guess would be that the molecule contains a ring . (We know this is the case, of course, but it’s nice to see the IR confirming what we already know).

This is what a 1-minute analysis of the IR of glucose can tell us. Not the whole structure, mind you, but certainly some important bits and pieces.

That’s enough for today. In the next post we’ll do some more 1-minute analyses and give more concrete examples of how to use the information in an IR spectrum to draw conclusions about molecular structure.

Related Articles

  • IR Spectroscopy: 4 Practice Problems
  • Bond Vibrations, Infrared Spectroscopy, and the “Ball and Spring” Model
  • Introduction To UV-Vis Spectroscopy
  • UV-Vis Spectroscopy: Practice Questions
  • UV-Vis Spectroscopy: Absorbance of Carbonyls
  • Degrees of Unsaturation (or IHD, Index of Hydrogen Deficiency)

More on the 3200 region: Amines, Amides, and Terminal Alkyne C-H

While we’re in the 3200 region…. Amines and Amides

examples of amine stretches in ir primary secondary and primary amide secondary amide

Amines and amides also have N-H stretches which show up in this region. [update: a comment from Paul Wenthold mentions some helpful advice about amides – they are rare – look for confirming evidence from the mass spectrum or other sources before assigning an amide based on a stretch in this region, as this region can also contain carbonyl “overtone” peaks]

Notice how the primary amine and primary amide have two “fangs”, while the secondary amine and secondary amide have a single peak.

The amine stretches tend to be sharper than the amide stretches; also the amides can be distinguished by a strong C=O stretch (see below).

Primary amines (click for spectra)

  • Benzylamine
  • Cyclohexylamine

Secondary amines:

  • N-methylbenzylamine
  • N,N-dibenzylamine
  • N-methylaniline

Primary amides

  • Propionamide

Secondary amides

  • N-methyl benzamide

Terminal alkyne C-H

Terminal alkynes have a characteristic C-H stretch around 3300 cm -1 . Here it is for ethynylbenzene, below.

  • Ethynylbenzene

triple bond ch stretch about 3400

00 General Chemistry Review

  • Lewis Structures
  • Ionic and Covalent Bonding
  • Chemical Kinetics
  • Chemical Equilibria
  • Valence Electrons of the First Row Elements
  • How Concepts Build Up In Org 1 ("The Pyramid")

01 Bonding, Structure, and Resonance

  • How Do We Know Methane (CH4) Is Tetrahedral?
  • Hybrid Orbitals and Hybridization
  • How To Determine Hybridization: A Shortcut
  • Orbital Hybridization And Bond Strengths
  • Sigma bonds come in six varieties: Pi bonds come in one
  • A Key Skill: How to Calculate Formal Charge
  • The Four Intermolecular Forces and How They Affect Boiling Points
  • 3 Trends That Affect Boiling Points
  • How To Use Electronegativity To Determine Electron Density (and why NOT to trust formal charge)
  • Introduction to Resonance
  • How To Use Curved Arrows To Interchange Resonance Forms
  • Evaluating Resonance Forms (1) - The Rule of Least Charges
  • How To Find The Best Resonance Structure By Applying Electronegativity
  • Evaluating Resonance Structures With Negative Charges
  • Evaluating Resonance Structures With Positive Charge
  • Exploring Resonance: Pi-Donation
  • Exploring Resonance: Pi-acceptors
  • In Summary: Evaluating Resonance Structures
  • Drawing Resonance Structures: 3 Common Mistakes To Avoid
  • How to apply electronegativity and resonance to understand reactivity
  • Bond Hybridization Practice
  • Structure and Bonding Practice Quizzes
  • Resonance Structures Practice

02 Acid Base Reactions

  • Introduction to Acid-Base Reactions
  • Acid Base Reactions In Organic Chemistry
  • The Stronger The Acid, The Weaker The Conjugate Base
  • Walkthrough of Acid-Base Reactions (3) - Acidity Trends
  • Five Key Factors That Influence Acidity
  • Acid-Base Reactions: Introducing Ka and pKa
  • How to Use a pKa Table
  • The pKa Table Is Your Friend
  • A Handy Rule of Thumb for Acid-Base Reactions
  • Acid Base Reactions Are Fast
  • pKa Values Span 60 Orders Of Magnitude
  • How Protonation and Deprotonation Affect Reactivity
  • Acid Base Practice Problems

03 Alkanes and Nomenclature

  • Meet the (Most Important) Functional Groups
  • Condensed Formulas: Deciphering What the Brackets Mean
  • Hidden Hydrogens, Hidden Lone Pairs, Hidden Counterions
  • Don't Be Futyl, Learn The Butyls
  • Primary, Secondary, Tertiary, Quaternary In Organic Chemistry
  • Branching, and Its Affect On Melting and Boiling Points
  • The Many, Many Ways of Drawing Butane
  • Wedge And Dash Convention For Tetrahedral Carbon
  • Common Mistakes in Organic Chemistry: Pentavalent Carbon
  • Table of Functional Group Priorities for Nomenclature
  • Summary Sheet - Alkane Nomenclature
  • Organic Chemistry IUPAC Nomenclature Demystified With A Simple Puzzle Piece Approach
  • Boiling Point Quizzes
  • Organic Chemistry Nomenclature Quizzes

04 Conformations and Cycloalkanes

  • Staggered vs Eclipsed Conformations of Ethane
  • Conformational Isomers of Propane
  • Newman Projection of Butane (and Gauche Conformation)
  • Introduction to Cycloalkanes (1)
  • Geometric Isomers In Small Rings: Cis And Trans Cycloalkanes
  • Calculation of Ring Strain In Cycloalkanes
  • Cycloalkanes - Ring Strain In Cyclopropane And Cyclobutane
  • Cyclohexane Conformations
  • Cyclohexane Chair Conformation: An Aerial Tour
  • How To Draw The Cyclohexane Chair Conformation
  • The Cyclohexane Chair Flip
  • The Cyclohexane Chair Flip - Energy Diagram
  • Substituted Cyclohexanes - Axial vs Equatorial
  • Ranking The Bulkiness Of Substituents On Cyclohexanes: "A-Values"
  • Cyclohexane Chair Conformation Stability: Which One Is Lower Energy?
  • Fused Rings - Cis-Decalin and Trans-Decalin
  • Naming Bicyclic Compounds - Fused, Bridged, and Spiro
  • Bredt's Rule (And Summary of Cycloalkanes)
  • Newman Projection Practice
  • Cycloalkanes Practice Problems

05 A Primer On Organic Reactions

  • The Most Important Question To Ask When Learning a New Reaction
  • Learning New Reactions: How Do The Electrons Move?
  • The Third Most Important Question to Ask When Learning A New Reaction
  • 7 Factors that stabilize negative charge in organic chemistry
  • 7 Factors That Stabilize Positive Charge in Organic Chemistry
  • Nucleophiles and Electrophiles
  • Curved Arrows (for reactions)
  • Curved Arrows (2): Initial Tails and Final Heads
  • Nucleophilicity vs. Basicity
  • The Three Classes of Nucleophiles
  • What Makes A Good Nucleophile?
  • What makes a good leaving group?
  • 3 Factors That Stabilize Carbocations
  • Equilibrium and Energy Relationships
  • What's a Transition State?
  • Hammond's Postulate
  • Learning Organic Chemistry Reactions: A Checklist (PDF)
  • Introduction to Free Radical Substitution Reactions
  • Introduction to Oxidative Cleavage Reactions

06 Free Radical Reactions

  • Bond Dissociation Energies = Homolytic Cleavage
  • Free Radical Reactions
  • 3 Factors That Stabilize Free Radicals
  • What Factors Destabilize Free Radicals?
  • Bond Strengths And Radical Stability
  • Free Radical Initiation: Why Is "Light" Or "Heat" Required?
  • Initiation, Propagation, Termination
  • Monochlorination Products Of Propane, Pentane, And Other Alkanes
  • Selectivity In Free Radical Reactions
  • Selectivity in Free Radical Reactions: Bromination vs. Chlorination
  • Halogenation At Tiffany's
  • Allylic Bromination
  • Bonus Topic: Allylic Rearrangements
  • In Summary: Free Radicals
  • Synthesis (2) - Reactions of Alkanes
  • Free Radicals Practice Quizzes

07 Stereochemistry and Chirality

  • Types of Isomers: Constitutional Isomers, Stereoisomers, Enantiomers, and Diastereomers
  • How To Draw The Enantiomer Of A Chiral Molecule
  • How To Draw A Bond Rotation
  • Introduction to Assigning (R) and (S): The Cahn-Ingold-Prelog Rules
  • Assigning Cahn-Ingold-Prelog (CIP) Priorities (2) - The Method of Dots
  • Enantiomers vs Diastereomers vs The Same? Two Methods For Solving Problems
  • Assigning R/S To Newman Projections (And Converting Newman To Line Diagrams)
  • How To Determine R and S Configurations On A Fischer Projection
  • The Meso Trap
  • Optical Rotation, Optical Activity, and Specific Rotation
  • Optical Purity and Enantiomeric Excess
  • What's a Racemic Mixture?
  • Chiral Allenes And Chiral Axes
  • Stereochemistry Practice Problems and Quizzes

08 Substitution Reactions

  • Introduction to Nucleophilic Substitution Reactions
  • Walkthrough of Substitution Reactions (1) - Introduction
  • Two Types of Nucleophilic Substitution Reactions
  • The SN2 Mechanism
  • Why the SN2 Reaction Is Powerful
  • The SN1 Mechanism
  • The Conjugate Acid Is A Better Leaving Group
  • Comparing the SN1 and SN2 Reactions
  • Polar Protic? Polar Aprotic? Nonpolar? All About Solvents
  • Steric Hindrance is Like a Fat Goalie
  • Common Blind Spot: Intramolecular Reactions
  • The Conjugate Base is Always a Stronger Nucleophile
  • Substitution Practice - SN1
  • Substitution Practice - SN2

09 Elimination Reactions

  • Elimination Reactions (1): Introduction And The Key Pattern
  • Elimination Reactions (2): The Zaitsev Rule
  • Elimination Reactions Are Favored By Heat
  • Two Elimination Reaction Patterns
  • The E1 Reaction
  • The E2 Mechanism
  • E1 vs E2: Comparing the E1 and E2 Reactions
  • Antiperiplanar Relationships: The E2 Reaction and Cyclohexane Rings
  • Bulky Bases in Elimination Reactions
  • Comparing the E1 vs SN1 Reactions
  • Elimination (E1) Reactions With Rearrangements
  • E1cB - Elimination (Unimolecular) Conjugate Base
  • Elimination (E1) Practice Problems And Solutions
  • Elimination (E2) Practice Problems and Solutions

10 Rearrangements

  • Introduction to Rearrangement Reactions
  • Rearrangement Reactions (1) - Hydride Shifts
  • Carbocation Rearrangement Reactions (2) - Alkyl Shifts
  • Pinacol Rearrangement
  • The SN1, E1, and Alkene Addition Reactions All Pass Through A Carbocation Intermediate

11 SN1/SN2/E1/E2 Decision

  • Identifying Where Substitution and Elimination Reactions Happen
  • Deciding SN1/SN2/E1/E2 (1) - The Substrate
  • Deciding SN1/SN2/E1/E2 (2) - The Nucleophile/Base
  • SN1 vs E1 and SN2 vs E2 : The Temperature
  • Deciding SN1/SN2/E1/E2 - The Solvent
  • Wrapup: The Quick N' Dirty Guide To SN1/SN2/E1/E2
  • Alkyl Halide Reaction Map And Summary
  • SN1 SN2 E1 E2 Practice Problems

12 Alkene Reactions

  • E and Z Notation For Alkenes (+ Cis/Trans)
  • Alkene Stability
  • Addition Reactions: Elimination's Opposite
  • Stereoselective and Stereospecific Reactions
  • Regioselectivity In Alkene Addition Reactions
  • Stereoselectivity In Alkene Addition Reactions: Syn vs Anti Addition
  • Hydrohalogenation of Alkenes and Markovnikov's Rule
  • Hydration of Alkenes With Aqueous Acid
  • Rearrangements in Alkene Addition Reactions
  • Halogenation of Alkenes and Halohydrin Formation
  • Oxymercuration Demercuration of Alkenes
  • Hydroboration Oxidation of Alkenes
  • m-CPBA (meta-chloroperoxybenzoic acid)
  • OsO4 (Osmium Tetroxide) for Dihydroxylation of Alkenes
  • Palladium on Carbon (Pd/C) for Catalytic Hydrogenation of Alkenes
  • Cyclopropanation of Alkenes
  • A Fourth Alkene Addition Pattern - Free Radical Addition
  • Alkene Reactions: Ozonolysis
  • Summary: Three Key Families Of Alkene Reaction Mechanisms
  • Synthesis (4) - Alkene Reaction Map, Including Alkyl Halide Reactions
  • Alkene Reactions Practice Problems

13 Alkyne Reactions

  • Acetylides from Alkynes, And Substitution Reactions of Acetylides
  • Partial Reduction of Alkynes With Lindlar's Catalyst
  • Partial Reduction of Alkynes With Na/NH3 To Obtain Trans Alkenes
  • Alkyne Hydroboration With "R2BH"
  • Hydration and Oxymercuration of Alkynes
  • Hydrohalogenation of Alkynes
  • Alkyne Halogenation: Bromination, Chlorination, and Iodination of Alkynes
  • Alkyne Reactions - The "Concerted" Pathway
  • Alkenes To Alkynes Via Halogenation And Elimination Reactions
  • Alkynes Are A Blank Canvas
  • Synthesis (5) - Reactions of Alkynes
  • Alkyne Reactions Practice Problems With Answers

14 Alcohols, Epoxides and Ethers

  • Alcohols - Nomenclature and Properties
  • Alcohols Can Act As Acids Or Bases (And Why It Matters)
  • Alcohols - Acidity and Basicity
  • The Williamson Ether Synthesis
  • Ethers From Alkenes, Tertiary Alkyl Halides and Alkoxymercuration
  • Alcohols To Ethers via Acid Catalysis
  • Cleavage Of Ethers With Acid
  • Epoxides - The Outlier Of The Ether Family
  • Opening of Epoxides With Acid
  • Epoxide Ring Opening With Base
  • Making Alkyl Halides From Alcohols
  • Tosylates And Mesylates
  • PBr3 and SOCl2
  • Elimination Reactions of Alcohols
  • Elimination of Alcohols To Alkenes With POCl3
  • Alcohol Oxidation: "Strong" and "Weak" Oxidants
  • Demystifying The Mechanisms of Alcohol Oxidations
  • Protecting Groups For Alcohols
  • Thiols And Thioethers
  • Calculating the oxidation state of a carbon
  • Oxidation and Reduction in Organic Chemistry
  • Oxidation Ladders
  • SOCl2 Mechanism For Alcohols To Alkyl Halides: SN2 versus SNi
  • Alcohol Reactions Roadmap (PDF)
  • Alcohol Reaction Practice Problems
  • Epoxide Reaction Quizzes
  • Oxidation and Reduction Practice Quizzes

15 Organometallics

  • What's An Organometallic?
  • Formation of Grignard and Organolithium Reagents
  • Organometallics Are Strong Bases
  • Reactions of Grignard Reagents
  • Protecting Groups In Grignard Reactions
  • Synthesis Problems Involving Grignard Reagents
  • Grignard Reactions And Synthesis (2)
  • Organocuprates (Gilman Reagents): How They're Made
  • Gilman Reagents (Organocuprates): What They're Used For
  • The Heck, Suzuki, and Olefin Metathesis Reactions (And Why They Don't Belong In Most Introductory Organic Chemistry Courses)
  • Reaction Map: Reactions of Organometallics
  • Grignard Practice Problems

16 Spectroscopy

  • Conjugation And Color (+ How Bleach Works)
  • Bond Vibrations, Infrared Spectroscopy, and the "Ball and Spring" Model
  • 1H NMR: How Many Signals?
  • Homotopic, Enantiotopic, Diastereotopic
  • Diastereotopic Protons in 1H NMR Spectroscopy: Examples
  • C13 NMR - How Many Signals
  • Liquid Gold: Pheromones In Doe Urine
  • Natural Product Isolation (1) - Extraction
  • Natural Product Isolation (2) - Purification Techniques, An Overview
  • Structure Determination Case Study: Deer Tarsal Gland Pheromone

17 Dienes and MO Theory

  • What To Expect In Organic Chemistry 2
  • Are these molecules conjugated?
  • Conjugation And Resonance In Organic Chemistry
  • Bonding And Antibonding Pi Orbitals
  • Molecular Orbitals of The Allyl Cation, Allyl Radical, and Allyl Anion
  • Pi Molecular Orbitals of Butadiene
  • Reactions of Dienes: 1,2 and 1,4 Addition
  • Thermodynamic and Kinetic Products
  • More On 1,2 and 1,4 Additions To Dienes
  • s-cis and s-trans
  • The Diels-Alder Reaction
  • Cyclic Dienes and Dienophiles in the Diels-Alder Reaction
  • Stereochemistry of the Diels-Alder Reaction
  • Exo vs Endo Products In The Diels Alder: How To Tell Them Apart
  • HOMO and LUMO In the Diels Alder Reaction
  • Why Are Endo vs Exo Products Favored in the Diels-Alder Reaction?
  • Diels-Alder Reaction: Kinetic and Thermodynamic Control
  • The Retro Diels-Alder Reaction
  • The Intramolecular Diels Alder Reaction
  • Regiochemistry In The Diels-Alder Reaction
  • The Cope and Claisen Rearrangements
  • Electrocyclic Reactions
  • Electrocyclic Ring Opening And Closure (2) - Six (or Eight) Pi Electrons
  • Diels Alder Practice Problems
  • Molecular Orbital Theory Practice

18 Aromaticity

  • Introduction To Aromaticity
  • Rules For Aromaticity
  • Huckel's Rule: What Does 4n+2 Mean?
  • Aromatic, Non-Aromatic, or Antiaromatic? Some Practice Problems
  • Antiaromatic Compounds and Antiaromaticity
  • The Pi Molecular Orbitals of Benzene
  • The Pi Molecular Orbitals of Cyclobutadiene
  • Frost Circles
  • Aromaticity Practice Quizzes

19 Reactions of Aromatic Molecules

  • Electrophilic Aromatic Substitution: Introduction
  • Activating and Deactivating Groups In Electrophilic Aromatic Substitution
  • Electrophilic Aromatic Substitution - The Mechanism
  • Ortho-, Para- and Meta- Directors in Electrophilic Aromatic Substitution
  • Understanding Ortho, Para, and Meta Directors
  • Why are halogens ortho- para- directors?
  • Disubstituted Benzenes: The Strongest Electron-Donor "Wins"
  • Electrophilic Aromatic Substitutions (1) - Halogenation of Benzene
  • Electrophilic Aromatic Substitutions (2) - Nitration and Sulfonation
  • EAS Reactions (3) - Friedel-Crafts Acylation and Friedel-Crafts Alkylation
  • Intramolecular Friedel-Crafts Reactions
  • Nucleophilic Aromatic Substitution (NAS)
  • Nucleophilic Aromatic Substitution (2) - The Benzyne Mechanism
  • Reactions on the "Benzylic" Carbon: Bromination And Oxidation
  • The Wolff-Kishner, Clemmensen, And Other Carbonyl Reductions
  • More Reactions on the Aromatic Sidechain: Reduction of Nitro Groups and the Baeyer Villiger
  • Aromatic Synthesis (1) - "Order Of Operations"
  • Synthesis of Benzene Derivatives (2) - Polarity Reversal
  • Aromatic Synthesis (3) - Sulfonyl Blocking Groups
  • Birch Reduction
  • Synthesis (7): Reaction Map of Benzene and Related Aromatic Compounds
  • Aromatic Reactions and Synthesis Practice
  • Electrophilic Aromatic Substitution Practice Problems

20 Aldehydes and Ketones

  • What's The Alpha Carbon In Carbonyl Compounds?
  • Nucleophilic Addition To Carbonyls
  • Aldehydes and Ketones: 14 Reactions With The Same Mechanism
  • Sodium Borohydride (NaBH4) Reduction of Aldehydes and Ketones
  • Grignard Reagents For Addition To Aldehydes and Ketones
  • Wittig Reaction
  • Hydrates, Hemiacetals, and Acetals
  • Imines - Properties, Formation, Reactions, and Mechanisms
  • All About Enamines
  • Breaking Down Carbonyl Reaction Mechanisms: Reactions of Anionic Nucleophiles (Part 2)
  • Aldehydes Ketones Reaction Practice

21 Carboxylic Acid Derivatives

  • Nucleophilic Acyl Substitution (With Negatively Charged Nucleophiles)
  • Addition-Elimination Mechanisms With Neutral Nucleophiles (Including Acid Catalysis)
  • Basic Hydrolysis of Esters - Saponification
  • Transesterification
  • Proton Transfer
  • Fischer Esterification - Carboxylic Acid to Ester Under Acidic Conditions
  • Lithium Aluminum Hydride (LiAlH4) For Reduction of Carboxylic Acid Derivatives
  • LiAlH[Ot-Bu]3 For The Reduction of Acid Halides To Aldehydes
  • Di-isobutyl Aluminum Hydride (DIBAL) For The Partial Reduction of Esters and Nitriles
  • Amide Hydrolysis
  • Thionyl Chloride (SOCl2)
  • Diazomethane (CH2N2)
  • Carbonyl Chemistry: Learn Six Mechanisms For the Price Of One
  • Making Music With Mechanisms (PADPED)
  • Carboxylic Acid Derivatives Practice Questions

22 Enols and Enolates

  • Keto-Enol Tautomerism
  • Enolates - Formation, Stability, and Simple Reactions
  • Kinetic Versus Thermodynamic Enolates
  • Aldol Addition and Condensation Reactions
  • Reactions of Enols - Acid-Catalyzed Aldol, Halogenation, and Mannich Reactions
  • Claisen Condensation and Dieckmann Condensation
  • Decarboxylation
  • The Malonic Ester and Acetoacetic Ester Synthesis
  • The Michael Addition Reaction and Conjugate Addition
  • The Robinson Annulation
  • Haloform Reaction
  • The Hell–Volhard–Zelinsky Reaction
  • Enols and Enolates Practice Quizzes
  • The Amide Functional Group: Properties, Synthesis, and Nomenclature
  • Basicity of Amines And pKaH
  • 5 Key Basicity Trends of Amines
  • The Mesomeric Effect And Aromatic Amines
  • Nucleophilicity of Amines
  • Alkylation of Amines (Sucks!)
  • Reductive Amination
  • The Gabriel Synthesis
  • Some Reactions of Azides
  • The Hofmann Elimination
  • The Hofmann and Curtius Rearrangements
  • The Cope Elimination
  • Protecting Groups for Amines - Carbamates
  • The Strecker Synthesis of Amino Acids
  • Introduction to Peptide Synthesis
  • Reactions of Diazonium Salts: Sandmeyer and Related Reactions
  • Amine Practice Questions

24 Carbohydrates

  • D and L Notation For Sugars
  • Pyranoses and Furanoses: Ring-Chain Tautomerism In Sugars
  • What is Mutarotation?
  • Reducing Sugars
  • The Big Damn Post Of Carbohydrate-Related Chemistry Definitions
  • The Haworth Projection
  • Converting a Fischer Projection To A Haworth (And Vice Versa)
  • Reactions of Sugars: Glycosylation and Protection
  • The Ruff Degradation and Kiliani-Fischer Synthesis
  • Isoelectric Points of Amino Acids (and How To Calculate Them)
  • Carbohydrates Practice
  • Amino Acid Quizzes

25 Fun and Miscellaneous

  • A Gallery of Some Interesting Molecules From Nature
  • Screw Organic Chemistry, I'm Just Going To Write About Cats
  • On Cats, Part 1: Conformations and Configurations
  • On Cats, Part 2: Cat Line Diagrams
  • On Cats, Part 4: Enantiocats
  • On Cats, Part 6: Stereocenters
  • Organic Chemistry Is Shit
  • The Organic Chemistry Behind "The Pill"
  • Maybe they should call them, "Formal Wins" ?
  • Why Do Organic Chemists Use Kilocalories?
  • The Principle of Least Effort
  • Organic Chemistry GIFS - Resonance Forms
  • Reproducibility In Organic Chemistry
  • What Holds The Nucleus Together?
  • How Reactions Are Like Music
  • Organic Chemistry and the New MCAT

26 Organic Chemistry Tips and Tricks

  • Common Mistakes: Formal Charges Can Mislead
  • Partial Charges Give Clues About Electron Flow
  • Draw The Ugly Version First
  • Organic Chemistry Study Tips: Learn the Trends
  • The 8 Types of Arrows In Organic Chemistry, Explained
  • Top 10 Skills To Master Before An Organic Chemistry 2 Final
  • Common Mistakes with Carbonyls: Carboxylic Acids... Are Acids!
  • Planning Organic Synthesis With "Reaction Maps"
  • Alkene Addition Pattern #1: The "Carbocation Pathway"
  • Alkene Addition Pattern #2: The "Three-Membered Ring" Pathway
  • Alkene Addition Pattern #3: The "Concerted" Pathway
  • Number Your Carbons!
  • The 4 Major Classes of Reactions in Org 1
  • How (and why) electrons flow
  • Grossman's Rule
  • Three Exam Tips
  • A 3-Step Method For Thinking Through Synthesis Problems
  • Putting It Together
  • Putting Diels-Alder Products in Perspective
  • The Ups and Downs of Cyclohexanes
  • The Most Annoying Exceptions in Org 1 (Part 1)
  • The Most Annoying Exceptions in Org 1 (Part 2)
  • The Marriage May Be Bad, But the Divorce Still Costs Money
  • 9 Nomenclature Conventions To Know
  • Nucleophile attacks Electrophile

27 Case Studies of Successful O-Chem Students

  • Success Stories: How Corina Got The The "Hard" Professor - And Got An A+ Anyway
  • How Helena Aced Organic Chemistry
  • From a "Drop" To B+ in Org 2 – How A Hard Working Student Turned It Around
  • How Serge Aced Organic Chemistry
  • Success Stories: How Zach Aced Organic Chemistry 1
  • Success Stories: How Kari Went From C– to B+
  • How Esther Bounced Back From a "C" To Get A's In Organic Chemistry 1 And 2
  • How Tyrell Got The Highest Grade In Her Organic Chemistry Course
  • This Is Why Students Use Flashcards
  • Success Stories: How Stu Aced Organic Chemistry
  • How John Pulled Up His Organic Chemistry Exam Grades
  • Success Stories: How Nathan Aced Organic Chemistry (Without It Taking Over His Life)
  • How Chris Aced Org 1 and Org 2
  • Interview: How Jay Got an A+ In Organic Chemistry
  • How to Do Well in Organic Chemistry: One Student's Advice
  • "America's Top TA" Shares His Secrets For Teaching O-Chem
  • "Organic Chemistry Is Like..." - A Few Metaphors
  • How To Do Well In Organic Chemistry: Advice From A Tutor
  • Guest post: "I went from being afraid of tests to actually looking forward to them".

Comment section

84 thoughts on “ infrared spectroscopy: a quick primer on interpreting spectra ”.

this quick guide is awesome, I’ve learned so much reading it. To recall whatever you forgot over time, this is the best option. Thank you

Glad you found it useful for refreshing your memory!

This has really been helpful for my studies in chemistry

I am glad you find it helpful Cirona!

This is very helpful

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Glad you find it helpful!

A lifesaver if there was ever one. Infrared Spectroscopy was so confusing for me in undergrad,and post grad had me even more muddled.One look at this article on the morning of the test was enough to make me take my test confidently and do it well! The way you simplified it while highlighting important points is crazy. I was trying to remember all the values given from the typical IR frequency table which wasn’t working at all and was leaving me anxious. Tongues and Swords made it so simple and memorable. Thanks for all that you do and more! This is Monica Rao all the way from India!

Glad to hear you found it useful! I had a similar experience in undergraduate and glad that this simplified things for you!

i love you, you just saved my life

explanation is very easy to understand. thank you

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This is so helpful thank you

Best Review on IR

Thank you Sagar.

Hi James, Thank you for your very clear tutorials on interpreting IR spectra. They have been really helpful to me.

I have a few questions regarding a compound with an unknown structure, which I am trying to decipher using FTIR. Would you be happy to have a look at this for me and confirm whether or not I have done it right, based on the information on your tutorials?

Thanks I am newbie and this finally made a pathway in my grey cells :)

Thanks a lot. This has really helped me I understood everything in it

Thank you so much for this great work. I have one problem: I used to work with polymers (in my particular case I am working with PVC films). Firstly, I do an FTIR spectrum of the “as received” PVC film. Next, I carry out a thermal treatment of the PVC film (below its Tg) and repeat the FTIR. The peaks have not change, however the intensity of them is different. I have tried to figure out an explanation for this phenomenon (searching in bibliography), but I didn´t found an answer. Do you have any idea of why this happen?

thank you very much.

You are absolutely amazing. I feel so happy and satisfied reading this. Your style of presenting the context is so good. Thank You for your hard work for us.

Thank you so much. Two month i have struggled about this topic. Full of detail in simple words with various example. Thank you again

I am really grateful this lesson is really awesome.

Thank you so much!! Your post really helped understangding IR :)

Thank you so much for this great information sir

Thank you!! This is so easy explained and helpful. I have one question: How much can I trust in my software suggestions? the software of my FTIR instrumen has some libraries included.

I’m not sure. There can be considerable variability between samples of the same molecule, depending on how the sample is prepared (thickness of film) and the amount of water present (which affects hydrogen bonding). The libraries are a good starting point but not a magic bullet, good when part of a more holistic approach to combine with other information (e.g. HRMS data)

Thanks Paul – I was unaware of the overtones in that region. Very helpful, thank you!

One thing you didn’t mention is the carbonyl overtone peaks, which result when the molecule absorbs two photons of IR light. These show up as weak peaks at 2 x the carbonyl frequency, so are in that 3300 – 3500 range.

It’s important know about this because beginning students very often assign those peaks to NH stretches. And it’s not crazy, because NH stretches in monosubstituted amides can be relatively weak, so it can be difficult to distinguish them.

This isn’t perfect, but, from an instructor perspective, my advice is to avoid the urge to assign them to amine or amide. If you see a carbonyl, expect to see that overtone and don’t call it an NH stretch. Now, this means you might miss an amide, but that alone is not sufficient to conclude it is amide. You would need to verify it by other means. As noted, amide C=O stretches tend to be lower energy than other functional groups, but even then I’d be careful about putting too fine a point on it (absorptions usually come in ranges, not in specific spots – the C=O is 1680: does that mean it’s amide? Could be, but it could also be a ketone at the edge of its range; it’s consistent with both). Now, if you have a mass spectrum that indicates the presence of a N (by having an odd molecular mass), so you know N is present, then sure, it could be NH stretching. But absent other information that indicates an amide, my advice is don’t go that direction.

This is the best review I have ever seen-splendid!

This is an excellent resource on IR for a newbie…love to give this to my students for reading. Looking for posts on mass spectrometry..

Thanks Anju – appreciate it. This is what I wish someone told me when I was learning how to interpret IR spectra.

Very clear, lots of examples and well thought out instructions. I feel so much more confident! Thank you soo much!!!

Great! So glad you feel more confident!

Symply excellent. Please, we need MOC Text book.

Not happening! But thank you

Seriously it is the best of all explanation I have seen ,it really helpful 💖

Very helpful. I can understand the materials much better

Thanks for the wonderful lecture, my question is how can one identify aromatic or the benzene ring absorption. Please I also need your email address

Look for the C-H bond stretch below 3000 cm-1. It is not specific for the aromatic ring but at least points to an sp2 hybridized carbon bonded to H.

saved my life honestly.

Honestly? Awesome!

Best explanation ever ! The only one I understood .. Thank you a lot!

Thanks Olivia! Glad you found it helpful!

I was completely lost at lecture on IR but after reading this, i realized its simple things made difficult. You saved me a failure.

So glad to hear it Josan.

Thanks! This article saved me. Recommended this to all my friends.

Thanks for letting me know Harshit!

Wow! Thanks – you will never know how much time this saved me.

So glad to hear it Freeman.

Excellent explanation! Thank you for all the hard work.

Thanks Zeke!

Thank you! you just saved my life

If it made IR less painful, that’s awesome Alejandra!

I see nothing about <500 cm-1 which is what I need to know

Really? I wish I had a better answer for you. The region below 500 cm-1 is an “enduring mystery” for many of us.

Loved this!!!!!


I know your faculty plans did not work out, but you are so better than many professors! Thank you! Never stop chasing your dreams!

Beautifully explained Sir !!

Best explanation of IR spectra I’ve came across. Waiting for your next post :)

I completely agree with the above posts. You should Youtube as well my friend. Great job!

I do have a Youtube channel but it has been quite neglected!

I COMPLETELY AGREE 100% with the previous praises and comments – you have been a SAVING grace in my organic chemistry understanding and I appreciate your approach in simplifying the most complex things. I have honestly spent 4+hrs in attempting 2 problems in figuring out the structures and feel so much better moving forward. THANK YOU! Keep up the phenomenal job!

Thank you Maribel!

Thanks for such a great focused article. It’s really very helpful.

Tried to make it useful. If it succeeded, great!

This is very clear and understandable even to a layman. Thanks a lot

You’re welcome!

why alkenes group (3000 -3100) & alkyl halides (500 -539) are added to NORYL (PPE + PS) plastic? which properties are affected?

How do you know the peak in the 3000-3100 isn’t from the styrene?

Thank you so much for this guide! Very thorough approach and great explanation.

Meg – so glad you’ve found it helpful. Put a lot of work into it!

Great work! best I could find in all these years in fact.

Never using another website or youtube vid (unless its yours) for help again. You’re amazing

Beautifully explained!

This is the best review for IR Spectroscopy out there!

THIS IS SO HELPFUL!! so many different examples were used and I understand everything now! Will there be a quick tutorial for carbon and proton NMR as well?

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Interpreting Infrared Spectra


Molecules have covalent bonds and have characteristic frequencies, these bonds rotate, bend and stretch continuously. If these bonds are given some energy i.e. infra-red radiation they will bend, rotate or stretch more vigorously and radiation of that frequency will be absorbed. Each bond in a molecule has its own frequency which it absorbs, when infra-red radiation is passed through a sample of an organic compound, some frequencies are absorbed, and some pass through without being absorbed. An infrared spectrum shows which frequencies were absorbed and which passed through, giving a unique “fingerprint” that can be used to identify the functional groups (fragments of molecules) of the molecules present. Below shows a typical infra-red spectrum.

ir peaks at 2200

The above graph shows a spectrum of Butan-2-ol, the y (vertical) axis shows the transmittance as a percentage and the x (horizontal) axis shows the wavenumber (in cm ‑1 ). If the transmittance is 100%, it means that all the light was transmitted through the sample and nothing was absorbed. So, for that frequency was not absorbed by your compound. However, if the transmittance is less than 100%, it means that some of the light was absorbed. This is known as a peak. Peaks are typically described by their intensity (strong, medium or weak) and by their peak width (sharp and broad). The table below shows sharp and broad peaks present from the infra-red spectrum above.

Different bonds with different functional groups absorb at different wavenumbers, the peaks shown in an infra-red spectrum is used to determine the different functional groups present in the molecule.

All organic compounds contain C-C and C-H bonds. Some peaks are very easy to recognise such as C=O and O-H bonds. Since many compounds contain C-H and C-C bonds, these peaks are almost always present in an infra-red spectrum: Any other bonds present, however, will give more distinctive peaks:

Identifying functional groups

Functional groups can be determined by the absorbed frequencies. Several examples of these characteristic absorptions are shown below.

1. Carbonyls (C=O) – Acetone

ir peaks at 2200

C=O is characterised by a sharp peak at 1715 cm -1 . Also found in carboxylic acids and esters.

2. Alcohols (C-O and O-H): Ethanol

ir peaks at 2200

O-H is characterised by a strong broad peak at 3200 – 3550 cm -1 . For C-O bond there is a sharp peak at 1050 cm -1 .

3. Carboxylic acids (C=O, C-O and O-H): Acetic Acid

ir peaks at 2200

O-H bond in carboxylic acid is characterised by a broad peak at 2500 – 3300 cm -1 . Notice that there are also sharp peaks at 1710 cm -1 C=O and 1300 cm -1 C-O.

4. Esters (C=O and C-O): Ethyl Acetate

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C-O is characterised by a sharp peak at 1210 cm -1 and 1750 cm -1 for C=O bond. (Note the absence of a broad peak between 2500 and 3500 cm -1 , thus no O-H bond present).

5. Hydrocarbons (C-C, C=C, C≡C): Heptane, Heptene and Heptyne

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Hydrocarbon compounds contain only C-H and C-C bonds, but there is plenty of information to be obtained from the infrared spectra arising from C-H stretching and C-H bending, depends on whether the C-C is single, double or triple bond as well as how long the molecular chain is.

6. Aromatic (C=C, C-H): Benzene

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The =C–H stretch in aromatics is observed at 3330-3335 cm -1 . Note this is higher frequency than is the –C–H stretch in alkanes. The C=C sharp peak can be found at 1550-1700 cm -1 .

7. Amide (C=O, N-H): Propanamide

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Amide is characterised by a strong C=O band at 1650 cm -1 (note this is below the carbonyl absorption for aldehyde and ketone). Absorptions for the NH (symmetric and asymmetric) band is in the range of 3200-3400 cm -1 . The broadness of the bands is likely due to hydrogen bonding.

8. Primary Amine (N-H, C-N): Propyl amine

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N-H is characterised by a medium peak at 660-900 cm -1 . C-N stretch is found at 1029-1200 cm -1 . Note the N-H bend which shows a symmetric and asymmetric band in the range of 3500 cm -1 .

9. Nitrile (C≡N): Propionitrile

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C≡N is characterised by the sharp peak at 2250 cm -1 . (Note this is in the same region as the alkyne C≡C)

Inorganic Compounds

Generally, the infrared bands for inorganic materials are broader, fewer in number and appear at lower wavenumbers than those observed for organic materials. If an inorganic compound forms covalent bonds within an ion, it can produce a characteristic infrared spectrum. Main infrared bands of some common inorganic ions:

Diatomic molecules produce one vibration along the chemical bond. Monatomic ligand, where metal s coordinate with atoms such as halogens, H, N or O, produce characteristic bands. These bands are summarized in below. Characteristic infrared bands of diatomic inorganic molecules: M(metal), X(halogen)

The fingerprint region The region of the spectrum which is mostly used to identify functional groups is between 1500 and 3500 cm -1 as most functional groups give characteristic absorptions in this region. The region between 500 – 1500 cm -1 of the spectrum is more complex and typically has a lot of peaks which are very close together and thus could be difficult to identify. These peaks are not from specific bonds but a result of the structure of the molecule as a whole. This region is completely differentfor each molecule structure even those with the same functional group. This region is identified as the fingerprint region. One of the most common application of infrared spectroscopy is to the identification of organic compounds. The major classes of organic molecules are shown in this article.


The following is a suggested strategy for determination of a molecular structure.

  • Concentrate on the 1500 and 3500 cm -1 regions first and on the typically functional groups.
  • Use a frequency table to identify the functional groups for each frequency
  • Use the fingerprint region (below 1500 cm -1 ) to confirm or elaborate on structural elements.
  • Do not try to assign every single peak in the spectrum
  • Cross check wherever possible
  • Take note of negative and positive evidence
  • In some cases, some band intensities may vary significantly for the same group.
  • If sample is in solution, some frequency bands are solvent-sensitive. Be cautious when using small wavenumber changes

Infra-red spectroscopy is a great identification of a sample if it is used in conjunction with other analytical methods such as nuclear magnetic resonance, mass spectroscopy and elemental analysis.

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A Process for Successful Infrared Spectral Interpretation


We wrap up our introduction to the theory of infrared spectral interpretation with a discussion of the correct process to follow when interpreting spectra. The author has developed this 12-step system over many years of interpreting spectra, and finds it gives him the best results. The process includes knowing how a spectrum was measured, systematically identifying peaks, and the proper use of infrared spectral interpretation aids. The answer to last column’s quiz is also disclosed.

Pages 14–21

Infrared (IR) spectral interpretation is firmly grounded in science as seen in the theory sections in previous installments. The challenge with interpreting spectra, however, is that with the hundreds of known functional groups that absorb in the mid-infrared and the resultant thousands of peaks, it becomes difficult to figure out what peaks are from what functional groups. To successfully interpret infrared spectra one must follow the right process, or else it is easy to be misled. This column will teach you a 12-step program that, if followed, should help you be more successful at interpreting spectra. The 12 steps are outlined below.

Step 1: Always Interpret Quality Spectra

The higher the quality of the spectrum you are working with, the easier your interpretation job will be. There are at least five attributes of a good spectrum: low noise, little or no baseline offset, a flat baseline, peaks on scale, and a lack of spectral artifacts.

An example of a bad spectrum is shown in Figure 1. Learn to eyeball the noise level in your spectra by looking at the amount of noise seen as “fuzz” in the baseline as indicated in Figure 1. If the noise is too large you may need to do more scans or re-prepare the sample.

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Q&A: Portable FT-IR Empowers On-Site Food Quality Assurance

Exploring the transformative capabilities of handheld Fourier transform infrared (FT-IR) spectrometers, Luis Rodriguez-Saona of The Ohio State University emphasizes their pivotal role in ensuring food integrity and safety across the entire supply chain.


Combining Spectroscopic and Chromatographic Techniques

An interview with Charles Wilkins, the winner of the 2013 American Chemical Society Division of Analytical Chemistry Award in Chemical Instrumentation, sponsored by the Dow Chemical Company.

Molecular structure illustration. Close up of blue chemical elements, background. | Image Credit: © ImageFlow -

Inorganics II: The Spectra

This column discusses the spectra of different inorganic functional groups, such as sulfates, carbonates, nitrates, silicates, and phosphates, with special attention being paid to the stretching and bending vibrations of the polyatomic anions in these compounds.


Bioprocess Monitoring with Ultrasound-Enhanced ATR Mid-IR Spectroscopy

Bernhard Lendl and Cosima Koch of the Vienna University of Technology have developed a new method for on-line monitoring of fermentations using mid-infrared spectroscopy.

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Identifying Insect Species Using Machine Learning

Scientists have created a new means of identifying insect species using ATR-FTIR spectroscopy and machine learning methods.

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Researchers Develop Efficient Nitroaromatic Compound Detection Method Using Novel Porous Polymers

Detecting nitroaromatic compounds is essential to preserve the environment. A recent study out of China saw the development of new conjugated porous polymers (CPPs) that could improve detection of these volatile compounds.

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Interpreting ir spectra.

Organic Chemistry

– IR spectra contain a wealth of information about the structures of compounds.

– We show some of the information that can be gathered from the spectra of octane and methylbenzene (commonly called toluene) in Figs.1 and 2.

Interpreting IR Spectra

– In this subject, we shall learn how to recognize the presence of characteristic IR absorption peaks that result from vibrations of alkyl and functional groups.

– The data given in the following Table will provide us with key information to use when correlating actual spectra with IR absorption frequencies that are typical for various groups.

Interpreting IR Spectra

IR Spectra of Hydrocarbons

Observation (1).

All hydrocarbons give absorption peaks in the 2800–3300 cm -1 region that are associated with carbon-hydrogen stretching vibrations.

– We can use these peaks in interpreting IR spectra because the exact location of the peak depends on the strength (and stiffness) of the C-H bond, which in turn depends on the hybridization state of the carbon that bears the hydrogen.

– The C-H bonds involving sp-hybridized carbon are the strongest and those involving sp 3 -hybridized carbon are the weakest.

– The order of bond strength is:

sp > sp 2 > sp 3

– This, too, is the order of the bond stiffness.

Observation (2)

The carbon-hydrogen stretching peaks of hydrogen atoms attached to sp-hybridized carbon atoms occur at the highest frequencies, about 3300 cm -1 .

– The carbon-hydrogen bond of a terminal alkyne (≡C-H) gives an absorption in the 3300 cm -1 region.

– We can see the absorption of the acetylenic (alkynyl) C-H bond of 1-heptyne at 3320 cm -1 in the following Figure.

Interpreting IR Spectra

Observation (3)

The carbon-hydrogen stretching peaks of hydrogen atoms attached to sp 2 -hybridized carbon atoms occur in the 3000–3100 cm -1 region.

– Thus, alkenyl C-H bonds and the C-H groups of aromatic rings give absorption peaks in this region.

– We can see the alkenyl C-H absorption peak at 3080 cm -1  in the spectrum of 1-octene (Fig. 4), and we can see the C-H absorption of the aromatic hydrogen atoms at 3090 cm -1  in the spectrum of methylbenzene (Fig. 2).

Interpreting IR Spectra

Observation (4)

The carbon-hydrogen stretching bands of hydrogen atoms attached to sp 3 -hybridized carbon atoms occur at the lowest frequencies, in the 2800–3000 cm -1 region.

– We can see methyl and methylene absorption peaks in the spectra of octane (Fig. 1), methylbenzene (Fig. 2), 1-heptyne (Fig. 3), and 1-octene (Fig. 4).

– Hydrocarbons also give absorption peaks in their IR spectra that result from carbon-carbon bond stretchings.

– Carbon-carbon single bonds normally give rise to very weak peaks that are usually of little use in assigning structures.

– More useful peaks arise from carbon-carbon multiple bonds, however.

Observation (5)

Carbon-carbon double bonds give absorption peaks in the 1620–1680 cm -1 region, and carbon-carbon triple bonds give absorption peaks between 2100 and 2260 cm -1 .

– These absorptions are not usually strong ones, and they are absent if the double or triple bond is symmetrically substituted. (No dipole moment change will be associated with the vibration.)

– The stretchings of the carbon-carbon bonds of benzene rings usually give a set of characteristic sharp peaks in the 1450–1600 cm -1 region.

Observation (6)

Absorptions arising from carbon-hydrogen bending vibrations of alkenes occur in the 600–1000 cm -1 region.

– With the aid of a spectroscopy handbook, the exact location of these peaks can often be used as evidence for the substitution pattern of the double bond and its configuration.

IR Spectra of Some Functional Groups Containing Heteroatoms

– Infrared spectroscopy gives us an invaluable method for recognizing quickly and simply the presence of certain functional groups in a molecule.

(1) IR Spectra of Carbonyl Functional Groups

– One important functional group that gives a prominent absorption peak in IR spectra is the carbonyl group, C=O.

– This group is present in aldehydes, ketones, esters , carboxylic acids, amides, and others.

– The carbon-oxygen double-bond stretching frequency of carbonyl groups gives a strong peak between 1630 and 1780 cm -1 .

– The exact location of the absorption depends on whether it arises from an aldehyde, ketone, ester, and so forth.

ir peaks at 2200

(2) IR Spectra of Alcohols and Phenols

– The hydroxyl groups of alcohols and phenols are also easy to recognize in IR spectra by their O-H stretching absorptions.

– These bonds also give us direct evidence for hydrogen bonding.

– The IR absorption of an alcohol or phenol O-H group is in the 3200–3550 cm -1 range, and most often it is broad.

– The typical broadness of the peak is due to the association of the molecules through hydrogen bonding, which causes a wider distribution of stretching frequencies for the O-H bond.

(a) If alcohol or phenol is present as a very dilute solution in a solvent that cannot contribute to hydrogen bonding (e.g., CCl 4 ), O-H absorption occurs as a very sharp peak in the 3590–3650 cm -1 region.

(b) In a very dilute solution in such a solvent or the gas phase, the formation of intermolecular hydrogen bonds does not take place because molecules of the analyte are too widely separated.

(c) A sharp peak in the 3590–3650 cm -1 region, therefore, is attributed to “free” (unassociated) hydroxyl groups.

(d) Increasing the concentration of the alcohol or phenol causes the sharp peak to be replaced by a broad band in the 3200–3550 cm -1 region.

– Hydroxyl absorptions in IR spectra of cyclohexylcarbinol (cyclohexylmethanol) run in dilute and concentrated solutions (Fig. 5) exemplify these effects.

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(3) IR Spectra of Carboxylic Acids

– The carboxylic acid group can also be detected by IR spectroscopy.

– If both carbonyl and hydroxyl stretching absorptions are present in an IR spectrum, there is good evidence for a carboxylic acid functional group (although it is possible that isolated carbonyl and hydroxyl groups could be present in the molecule).

– The hydroxyl absorption of a carboxylic acid is often very broad, extending from 3600 cm -1 to 2500 cm -1 .

– Figure 6 shows the IR spectrum of propanoic acid.

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(4) IR Spectra of Amines

– IR spectroscopy also gives evidence for N-H bonds (see Figure).

Interpreting IR Spectra

(a) Primary (1 o ) and secondary (2 o ) amines give absorptions of moderate strength in the 3300–3500 cm -1 region.

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(b) Primary amines exhibit two peaks in this region due to symmetric and asymmetric stretching of the two N-H bonds.

(c) Secondary amines exhibit a single peak.

(d) Tertiary amines show no N-H absorption because they have no such bond.

(e) A basic pH is evidence for any class of amine.

– Hydrogen bonding causes N-H stretching peaks of 1 o and 2 o amines to broaden.

– The NH groups of amides give similar absorption peaks and include a carbonyl absorption as well.

Solved Problems on Interpreting IR Spectra

(1) A compound with the molecular formula C 4 H 4 O 2  has a strong sharp absorbance near 3300 cm -1 , absorbances in the 2800–3000 cm -1 region, and a sharp absorbance peak near 2200 cm-1. It also has a strong broad absorbance in the 2500–3600 cm -1 region and a strong peak in the 1710–1780 cm -1 region. Propose a possible structure for the compound.

Strategy and Answer:

– The sharp peak near 3300 cm -1 is likely to arise from the stretching of hydrogen attached to the sp-hybridized carbon of a triple bond.

– The sharp peak near 2200 cm -1 , where the triple bond of an alkyne stretches, is consistent with this.

– The peaks in the 2800–3000 cm -1 region suggest stretchings of the C-H bonds of alkyl groups, either CH 2 or CH 3 groups.

– The strong, broad absorbance in the 2500–3600 cm -1 region suggests a hydroxyl group arising from a carboxylic acid.

– The strong peak around 1710–1780 cm -1 is consistent with this since it could arise from the carbonyl group of a carboxylic acid.

– Putting all this together with the molecular formula suggests the compound is:

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(2) What key peaks would you expect to find in the IR spectrum of the following compound?

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– The compound is an amide.

– We should expect a strong peak in the 1630–1690 cm -1 region arising from the carbonyl group and a single peak of moderate strength in the 3300–3500 cm -1 region for the N-H group.

Reference: Organic chemistry / T.W. Graham Solomons, Craig B.Fryhle, Scott A. Snyder, / ( eleventh edition) / 2014.

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First refuelling for Russia’s Akademik Lomonosov floating NPP


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The FNPP includes two KLT-40S reactor units. In such reactors, nuclear fuel is not replaced in the same way as in standard NPPs – partial replacement of fuel once every 12-18 months. Instead, once every few years the entire reactor core is replaced with and a full load of fresh fuel.

The KLT-40S reactor cores have a number of advantages compared with standard NPPs. For the first time, a cassette core was used, which made it possible to increase the fuel cycle to 3-3.5 years before refuelling, and also reduce by one and a half times the fuel component in the cost of the electricity produced. The operating experience of the FNPP provided the basis for the design of the new series of nuclear icebreaker reactors (series 22220). Currently, three such icebreakers have been launched.

The Akademik Lomonosov was connected to the power grid in December 2019, and put into commercial operation in May 2020.

Electricity generation from the FNPP at the end of 2023 amounted to 194 GWh. The population of Pevek is just over 4,000 people. However, the plant can potentially provide electricity to a city with a population of up to 100,000. The FNPP solved two problems. Firstly, it replaced the retiring capacities of the Bilibino Nuclear Power Plant, which has been operating since 1974, as well as the Chaunskaya Thermal Power Plant, which is more than 70 years old. It also supplies power to the main mining enterprises located in western Chukotka. In September, a 490 km 110 kilovolt power transmission line was put into operation connecting Pevek and Bilibino.

Image courtesy of TVEL

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11.5: Infrared Spectra of Some Common Functional Groups

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Common Group Frequencies Summary

When analyzing an IR spectrum, it is helpful to overlay the diagram below onto the spectrum with our mind to help recognize functional groups.

The region of the infrared spectrum from 1200 to 700 cm -1 is called the fingerprint region. This region is notable for the large number of infrared bands that are found there. Many different vibrations, including C-O, C-C and C-N single bond stretches, C-H bending vibrations, and some bands due to benzene rings are found in this region. The fingerprint region is often the most complex and confusing region to interpret, and is usually the last section of a spectrum to be interpreted. However, the utility of the fingerprint region is that the many bands there provide a fingerprint for a molecule.

Group Frequencies - a closer look

Detailed information about the infrared absorptions observed for various bonded atoms and groups is usually presented in tabular form. The following table provides a collection of such data for the most common functional groups. Following the color scheme of the chart, stretching absorptions are listed in the blue-shaded section and bending absorptions in the green shaded part. More detailed descriptions for certain groups (e.g. alkenes, arenes, alcohols, amines & carbonyl compounds) may be viewed by clicking on the functional class name . Since most organic compounds have C-H bonds, a useful rule is that absorption in the 2850 to 3000 cm -1 is due to sp 3 C-H stretching; whereas, absorption above 3000 cm -1 is from sp 2 C-H stretching or sp C-H stretching if it is near 3300 cm -1 .

Recognizing Group Frequencies in IR Spectra - a very close look


Hydrocarbons compounds contain only C-H and C-C bonds, but there is plenty of information to be obtained from the infrared spectra arising from C-H stretching and C-H bending.

In alkanes, which have very few bands, each band in the spectrum can be assigned:

  • C–H stretch from 3000–2850 cm -1
  • C–H bend or scissoring from 1470-1450 cm -1
  • C–H rock, methyl from 1370-1350 cm -1
  • C–H rock, methyl, seen only in long chain alkanes, from 725-720 cm -1

Figure 3. shows the IR spectrum of octane. Since most organic compounds have these features, these C-H vibrations are usually not noted when interpreting a routine IR spectrum. Note that the change in dipole moment with respect to distance for the C-H stretching is greater than that for others shown, which is why the C-H stretch band is the more intense.

octane (1).png

In alkenes compounds, each band in the spectrum can be assigned:

  • C=C stretch from 1680-1640 cm -1
  • =C–H stretch from 3100-3000 cm -1
  • =C–H bend from 1000-650 cm -1

Figure 4. shows the IR spectrum of 1-octene. As alkanes compounds, these bands are not specific and are generally not noted because they are present in almost all organic molecules.


In alkynes, each band in the spectrum can be assigned:

  • –C?C– stretch from 2260-2100 cm -1
  • –C?C–H: C–H stretch from 3330-3270 cm -1
  • –C?C–H: C–H bend from 700-610 cm -1

The spectrum of 1-hexyne, a terminal alkyne, is shown below.


In aromatic compounds, each band in the spectrum can be assigned:

  • C–H stretch from 3100-3000 cm -1
  • overtones, weak, from 2000-1665 cm -1
  • C–C stretch (in-ring) from 1600-1585 cm -1
  • C–C stretch (in-ring) from 1500-1400 cm -1
  • C–H "oop" from 900-675 cm -1

Note that this is at slightly higher frequency than is the –C–H stretch in alkanes. This is a very useful tool for interpreting IR spectra. Only alkenes and aromatics show a C–H stretch slightly higher than 3000 cm -1 .

Figure 6. shows the spectrum of toluene.


Functional Groups Containing the C-O Bond

Alcohols have IR absorptions associated with both the O-H and the C-O stretching vibrations.

  • O–H stretch, hydrogen bonded 3500-3200 cm -1
  • C–O stretch 1260-1050 cm -1 (s)

Figure 7. shows the spectrum of ethanol. Note the very broad, strong band of the O–H stretch.


The carbonyl stretching vibration band C=O of saturated aliphatic ketones appears:

  • C=O stretch - aliphatic ketones 1715 cm -1

- ?, ?-unsaturated ketones 1685-1666 cm -1

Figure 8. shows the spectrum of 2-butanone. This is a saturated ketone, and the C=O band appears at 1715.


If a compound is suspected to be an aldehyde, a peak always appears around 2720 cm -1 which often appears as a shoulder-type peak just to the right of the alkyl C–H stretches.

  • H–C=O stretch 2830-2695 cm -1
  • aliphatic aldehydes 1740-1720 cm -1
  • alpha, beta-unsaturated aldehydes 1710-1685 cm -1

Figure 9. shows the spectrum of butyraldehyde.


The carbonyl stretch C=O of esters appears:

  • aliphatic from 1750-1735 cm -1
  • ?, ?-unsaturated from 1730-1715 cm -1
  • C–O stretch from 1300-1000 cm -1

Figure 10. shows the spectrum of ethyl benzoate.

ethyl benzoate.png

The carbonyl stretch C=O of a carboxylic acid appears as an intense band from 1760-1690 cm -1 . The exact position of this broad band depends on whether the carboxylic acid is saturated or unsaturated, dimerized, or has internal hydrogen bonding.

  • O–H stretch from 3300-2500 cm -1
  • C=O stretch from 1760-1690 cm -1
  • C–O stretch from 1320-1210 cm -1
  • O–H bend from 1440-1395 and 950-910 cm -1

Figure 11. shows the spectrum of hexanoic acid.

hexanoic acid.png

Organic Nitrogen Compounds

  • N–O asymmetric stretch from 1550-1475 cm -1
  • N–O symmetric stretch from 1360-1290 cm -1


Organic Compounds Containing Halogens

Alkyl halides are compounds that have a C–X bond, where X is a halogen: bromine, chlorine, fluorene, or iodine.

  • C–H wag (-CH 2 X) from 1300-1150 cm -1
  • C–Cl stretch 850-550 cm -1
  • C–Br stretch 690-515 cm -1

The spectrum of 1-chloro-2-methylpropane are shown below.


For more Infrared spectra Spectral database of organic molecules is introduced to use free database. Also, the infrared spectroscopy correlation table is linked on bottom of page to find other assigned IR peaks.

1. What functional groups give the following signals in an IR spectrum?

A) 1700 cm -1

B) 1550 cm -1

C) 1700 cm -1 and 2510-3000 cm -1

2. How can you distinguish the following pairs of compounds through IR analysis?

A) CH 3 OH (Methanol) and CH 3 CH 2 OCH 2 CH 3 (Diethylether)

B) Cyclopentane and 1-pentene.

3. The following spectra is for the accompanying compound. What are the peaks that you can I identify in the spectrum?

Source: SDBSWeb : (National Institute of Advanced Industrial Science and Technology, 2 December 2016)

4. What absorptions would the following compounds have in an IR spectra?

A) A OH peak will be present around 3300 cm -1 for methanol and will be absent in the ether.

B) 1-pentene will have a alkene peak around 1650 cm -1 for the C=C and there will be another peak around 3100 cm -1 for the sp 2 C-H group on the alkene

C) Cannot distinguish these two isomers. They both have the same functional groups and therefore would have the same peaks on an IR spectra.

Frequency (cm-1) Functional Group

3200 C≡C-H

2900-3000 C-C-H, C=C-H

2100 C≡C

(There is also an aromatic undertone region between 2000-1600 which describes the substitution on the phenyl ring.)

3300 (broad) O-H

2000-1800 Aromatic Overtones

Contributors and Attributions

Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University )

Prof. Steven Farmer ( Sonoma State University )

William Reusch, Professor Emeritus ( Michigan State U. ), Virtual Textbook of Organic Chemistry


Moscow Sky Lights Up With Strange Glow After Explosion at Electrical Substation: Reports

N ew footage has emerged showing bright flashes lighting up the night sky in southern Moscow during the early morning hours of November 22. has learned that there was an explosion at an electrical substation on the outskirts of Russia's capital city followed by an alleged power outage in "several" homes.

Video snippets, shared on Russian news channels like ASTRA , captured a series of flashes that caused the sky to change color. Smoke could also be seen rising from a building.

Corroborating the video, several Russian Telegram accounts reported an explosion near the south of Moscow and a subsequent fire at the Lyublino electrical substation, southeast of central Moscow, per Newsweek .

The local authorities from the area have since confirmed that an explosion occurred in the village of Molokovo, but they reassured the public that all vital facilities were operating as normal.

Russian outlet reported the blaze at the substation and noted “several” power outages.

The town of Lytkarino, located to the southeast of Moscow, was one of the affected areas, as reported by the independent outlet, Meduza .

Additional power failures were reported in the southern Domodedovo section of the city. However, electricity was later restored to these areas.

One local resident speculated that a drone may have been responsible for the explosion, but additional sources are yet to support this theory.

Newsweek reported that messages on the ASTRA Telegram account run by independent Russian journalists showed residents near the substation panicking. One concerned Russian called it a "nightmare."

The incident follows an attack by Russia on a power station in southwestern Ukraine that left 2,000 people without electricity . reported previously:

“ Russian forces launched a total of 38 Iranian-made Shahed-136/131 drones during the later hours of November 17 and 18.

The Ukrainian Air Force Command reported that 29 of these drones were shot down [...].

One civilian was injured as a result of the attack that targeted energy infrastructure in the southwestern Odesa Oblast.”

The assault came after repeated warnings by Ukraine’s President Volodymyr Zelensky that Russia would try to cripple its power grid as winter approaches.

Ukraine's leader warned that if Russia resorted to attacking its power utilities, it would respond in kind.

Ukraine has conducted numerous long-range aerial drone strikes on Moscow since May 2023.

Most recently on November 20, it was reported that one such incursion was intercepted close to the city, per Kyiv Post .

Moscow’s Mayor Sergei Sobyanin confirmed this and elaborated that the region's air defense systems intercepted the unmanned craft over the city of Elektrostal to the east of Moscow, as well as another over the Bogorodsky district, northeast of central Moscow.

The details of the recently surfaced video footage have yet to be independently verified.

The Moscow skyline lit up on November 22 causing panic. By: Meduza

نگاهی به مترو روسیه

اگر از مسافران تور روسیه در مورد جاذبه‌های این کشور سوال کنید، یکی از مواردی که حتما از آن نام می‌برند مترو روسیه است! شاید تعجب‌آور باشد که مترو روسیه و ایستگاه‌های آن به یکی از دیدنی‌‌ترین نقاط این کشور تبدیل شده‌ است اما با دیدن این ویدئو احتمالا هر کسی شیفته این ایستگاه‌های جذاب مترو روسیه می‌شود.

مترو روسیه، جاذبه‌های زیرزمینی

جاهای دیدنی مسکو ، بسیار است و به تمام این دیدنی‌ها باید، ایستگاه‌های مترو شهری را هم اضافه کرد. مترو روسیه از آن دست جذابیت‌های دیدنی، زیر پوست شهر است. مترو در مسکو، 14 خط و 212 ایستگاه دارد و از بین این 212 ایستگاه، 44 ایستگاه در بطن اماکن تاریخی قرار گرفته است یا بهتر بگوییم خود یک موزه تاریخی جذاب است. به همین دلیل هم هست که بسیاری از مسافران تور مسکو از مترو برای گردش‌ و پرسه در شهر استفاده می‌کنند.

برای نمونه، ایستگاه میدان انقلاب در مترو روسیه که با مجسمه‌های برنزی از شخصیت‌های انقلابی روسیه پر شده است یا ایستگاه کیفسکا مترو روسیه، که با طراحی ویژه و باشکوه و تزئینات زیبای خود در فهرست 10 ایستگاه مترو برتر دنیا قرار گرفته است. زیبایی و طراحی ویژه این ایستگاه‌ مترو روسیه، جا به جا شدن با قطار‌‌های متروی شهری را به حرکت در تونل تاریخ و زمان شبیه کرده است و همین حس و حال و جذابیت هم، مترو روسیه را حسابی سر زبان‌ها انداخته است. 

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ir peaks at 2200

لست‌سکند در سال 89 با هدف ارائه خدمات متفاوت و با کیفیت به شما عزیزان در صنعت گردشگری تاسیس شده است. سیاست اصلی سایت، ارائه اطلاعات کامل و صحیح و بدون جهت گیری و جانب داری و بدون واسطه میباشد. همچنین اشتراک گذاری تجارب مسافران در بخشهای مختلف از ویژگیهای بارز و خاص سایت محسوب میشود و با استقبال بسیار زیاد کاربران نیز مواجه شده است.

تمامی حقوق این وبگاه از آنِ لست‌سکند است. | 1389 - 1402

خانواده لست‌سکند



  1. (a) FTIR peak position at 2200 cm -1 and (b) Corresponding relative

    ir peaks at 2200

  2. Ir Spectrum Peak Chart

    ir peaks at 2200

  3. Ir Spectra Peaks Chart

    ir peaks at 2200

  4. How To Read IR Spectra: 7 Easy Steps

    ir peaks at 2200

  5. Infrared Spectroscopy

    ir peaks at 2200

  6. Ir Spectrum Table Of Peaks

    ir peaks at 2200


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  1. Infrared spectroscopy correlation table

    An infrared spectroscopy correlation table (or table of infrared absorption frequencies) is a list of absorption peaks and frequencies, typically reported in wavenumber, for common types of molecular bonds and functional groups.

  2. 4.5 IR Data Table

    From there, a data table of approximate frequencies for different types of bonds has been created to use to help IR spectrum analysis. Table of Common IR Absorptions. Note: strong, medium, weak refers to the length of the peak (in the y axis direction). Note: spectra taken by ATR method (used at CSB/SJU) have weaker peaks between 4000-2500 cm ...

  3. PDF IR Tables, UCSC

    Characteristic IR Absorption Peaks of Functional Groups* Vibration Position (cm-1) Intensity* Notes Alkanes C-H stretch 2990 - 2850 m to s Alkenes ... C≡N stretch 2280 -2200 s Aldehydes C-H stretch 2900 - 2800 & 2800 - 2700 s H-C=O Fermi doublet C=O stretch 1740 - 1720 (sat.) 1715 - 1680 (conj.)

  4. 6.3: IR Spectrum and Characteristic Absorption Bands

    The wavenumber is defined as the reciprocal of wavelength ( Formula 6.3 ), and the wavenumbers of infrared radiation are normally in the range of 4000 cm -1 to 600 cm -1 (approximate corresponds the wavelength range of 2.5 μm to 17 μm of IR radiation). Formula 6.3 Wavenumber. Please note the direction of the horizontal axis (wavenumber) in IR ...

  5. IR Absorption Table

    1780 - 1710 (s) 1690 - 1630 (s) The carbonyl stretching absorption is one of the strongest IR absorptions, and is very useful in structure determination as one can determine both the number of carbonyl groups (assuming peaks do not overlap) but also an estimation of which types. Amide N-H Stretch. 3700 - 3500 (m)

  6. IR handout

    IR handout. From this equation, one can deduce some basic trends can be deducted: a. If the force constant F (= bond strength) increases, the stretching frequency will increase as well (in cm. belongs to saturated systems (alkanes, sp ), while the peaks from 3000-3100 cm example 2; aromatic ring, . The differences in wavenumbers are mainly due ...

  7. Interpreting IR Specta: A Quick Guide

    A peak in the region around 2200 cm-1 - 2050 cm-1 is a subtle indicator of the presence of a triple bond [C≡N or C≡C] . Nothing else shows up in this region. ... the C=O stretch is almost always the strongest peak in the IR spectrum and impossible to miss. The position of the C=O stretch varies slightly by carbonyl functional group. Some ...

  8. Infrared Spectroscopy Absorption Table

    The following table lists infrared spectroscopy absorptions by frequency regions. 4000-3000 cm -1. 3700-3584. medium. sharp.

  9. PDF Guide for Infrared Spectroscopy

    IR-Window Material Infrared Tables 2 3 Near Infrared Table 5 Sources 6 Detectors Beamsplitters Conversion Table of Energy and Wavelength Units for Far and Mid Infrared Conversion Table of Energy and Wavelength Units for Near Infrared, Visible and UV 7 8 9 10 Conversion Table of Transmittance and Absorbance Units 11

  10. Interpreting Infrared Spectra

    Introduction to Infrared Spectroscopy. Learn how to interpret spectra in a simply and intuitive way.


    Hydrocarbons show IR absorption peaks between 2800 and 3300 cm-1 due to C-H stretching vibrations. The hybridization of the carbon affects the exact position of the ... The CN triple bond absorption appears at 2200-2300 cm-1, in about the same place as the CC triple bond absorption. Both of these bands are usually medium to weak in intensity.

  12. A Process for Successful Infrared Spectral Interpretation

    Triple bonds such as C≡N and C≡C have stretching peaks around 2200 cm-1. The strong peak in this region in Figure 5 is from a nitrile (C≡N) bond. ... First, many functional groups have multiple peaks in the mid-IR, and tracking down as many peaks as possible for them raises the probability of a correct interpretation. Second, these bands ...

  13. Fourier Transform Infrared Spectroscopy (FT-IR): Broad peak from 2000

    What can be the explanation for a broad peak from 2000 to 2300 cm-1 in an infrared spectrum? The samples I'm testing are electrodeposited chitosan thin films. In the spectra I can identify the...

  14. A peak at around ~2200 cm-1 keeps appearing in my amino acid IR spectra

    A peak at around ~2200 cm-1 keeps appearing in my amino acid IR spectra. What bond can I assign this to? I'm dealing with amino acid spectra and a peak at 2200 keeps appearing. To what...

  15. 12.7: Interpreting Infrared Spectra

    The key absorption peak in this spectrum is that from the carbonyl double bond, at 1716 cm-1 (corresponding to a wavelength of 5.86 mm, ... Alkynes have characteristic IR absorbance peaks in the range of 2100-2250 cm-1 due to stretching of the carbon-carbon triple bond, ...

  16. What is this peak at 2300 cm-1?

    Hi Libby, I think your peak is not located at 2300 cm-1 but between 2300 - 2200 cm-1 or more precisely located at 2270 - 2280 cm-1 which is corresponding to isocyanate group of vibration...

  17. Interpreting IR Spectra

    - The sharp peak near 2200 cm-1, where the triple bond of an alkyne stretches, is consistent with this. - The peaks in the 2800-3000 cm-1 region suggest stretchings of the C-H bonds of alkyl groups, either CH 2 or CH 3 groups. - The strong, broad absorbance in the 2500-3600 cm-1 region suggests a hydroxyl group arising from a ...

  18. PDF Sintering of Industrial Uranium Dioxide Pellets Using Microwave

    The container was installed in the resonator in such a way that the viewing axis of the IR pyrometer coincided with the hole on its upper horizontal wall. In the resonator, air was evacuated through the corresponding valves, and a gas reducing mixture of argon with 7% hydrogen (TU 2114-002-05015259-97, JSC "Linde Gas Rus") was supplied to ...

  19. Does FT-IR Absorption around 2300

    Popular answers (1) Check in free NIST database. Generally each program used to FTIR data acquisition has a possibility to compensation CO2 and water. Try to find this option.

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    Rosatom's fuel company TVEL has supplied nuclear fuel for reactor 1 of the world's only floating NPP (FNPP), the Akademik Lomonosov, moored at the city of Pevek, in Russia's Chukotka Autonomous Okrug. The supply of fuel was transported along the Northern Sea Route. The first ever refuelling of the FNPP is planned to begin before the end of ...

  21. 11.5: Infrared Spectra of Some Common Functional Groups

    B) 1-pentene will have a alkene peak around 1650 cm-1 for the C=C and there will be another peak around 3100 cm-1 for the sp 2 C-H group on the alkene. C) Cannot distinguish these two isomers. They both have the same functional groups and therefore would have the same peaks on an IR spectra. 3. Frequency (cm-1) Functional Group. 3200 C≡C-H

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    New footage has emerged showing bright flashes lighting up the night sky in southern Moscow during the early morning hours of November 22. has learned that there was an explosion at an ...

  23. نگاهی به مترو روسیه

    مترو روسیه، جاذبه‌های زیرزمینی. جاهای دیدنی مسکو ، بسیار است و به تمام این دیدنی‌ها باید، ایستگاه‌های مترو شهری را هم اضافه کرد. مترو روسیه از آن دست جذابیت‌های دیدنی، زیر پوست شهر است ...