Core Concepts
This article will provide a table containing the IR spectrum frequency values and the molecules they represent.
Topics Covered in other Articles
Table of IR Spectrum Frequency Values
IR Spectrum Stretching Vibrations
| Bond Order | Frequency | Structural Unit | Appearance of the Peak |
| Single Bonds | 3200–3600 | O-H (Alcohol) | Broad |
| 2500–3350 | O-H (Carboxylic acids) | Broad and zig-zagged | |
| 3300–3500 | N-H (Primary or secondary Amine) | Broad Primary amines display 2 peaks, because they have 2 N-H bonds Secondary amines display only 1 peak (1 N-H bond) | |
| 3310–3320 | C-H (Alkane) | – | |
| 3000–3100 | C-H (Alkene) | – | |
| 2850–2950 | C-H (Alkyne) | Sharp | |
| 2695-2830 | C-H (Aldehyde) | Doublet | |
| 2800-3000 | N-H (Amine Salt) | – | |
| 2550-2600 | S-H (Thiol) | Weak | |
| 1500-1550 | N-O (nitro compound) | Strong | |
| 1200 | C-O (sp2 carbon) | – | |
| 1025–1200 | C-O (sp3 carbon) | – | |
| 1000-1400 | C-F (fluoro compound) | Strong | |
| 550-850 | C-Cl stretching | Strong | |
| 515-690 | C-Br stretching | Strong | |
| 600500- | C-I stretching | Strong | |
| Double Bonds | 1740–1790 and 1800–1850 | C=O (Acid anhydrides) | Strong and very sharp |
| 1770–1815 | C=O (Acyl halides) | Strong and very sharp | |
| 1760 | C=O (Carboxylic acid monomer) | Strong | |
| 1730–1750 | C=O (Esters) | Strong and very sharp | |
| 1720-1740 | C=O (Aldehyde) | Strong | |
| 1715-1730 | C=O (α,β-unsaturated ester) | Strong | |
| 1710–1750 | C=O (Carbonyl carbon in aldehydes and ketones) | Strong and very sharp | |
| 1705-1725 | C=O (Aliphatic ketone) | Strong | |
| 1700–1720 | C=O (Carboxylic acid dimer) | Strong and very sharp | |
| 1690 | C=O (Primary Amides) | Strong | |
| 1685-1710 | C=O (Conjugated Aldehyde) | Strong | |
| 1680 | C=O (Secondary or Tertiary Amides) | Strong and very sharp | |
| 1666-1685 | C=O (Conjugated ketone) | Strong | |
| 1640-1690 | C=N ( imine / oxime ) | Medium | |
| 1380-1415 | S=O (sulfate) | Strong | |
| 1380-1410 | S=O (sulfonyl chloride) | Strong | |
| 1342-1350 | S=O (sulfonic acid) | Strong | |
| 1335-1372 | S=O (sulfonate) | Strong | |
| 1335-1370 | S=O (sulfonamide) | Strong | |
| 1300-1350 | S=O (sulfone) | Strong | |
| 1030-1070 | S=O (sulfoxide) | Strong | |
| Triple Bonds | 2240–2280 | C≡N (Nitrile) | Weak |
| 2175-2140 | S-C≡N (thiocyanate) | Strong | |
| 2190–2260 | C≡C (Disubstituted Alkyne) | Weak | |
| 2100-2140 | C≡C (Monosubstituted Alkyne) | Weak |
IR Spectrum Bending Vibrations
| Classification | Frequency | Structural Unit | Appearance of the Peak |
| Alkenes | 910, 990 | C=C bending Monosubstituted terminal alkene RCH=CH2 | – |
| 890 | C=C bending Disubstituted terminal alkene R2C=CH2 | – | |
| 960–980 | C=C bending Disubstituted trans alkene trans RCH=CHR’ | Strong | |
| 790–840 | C=C bending Trisubstituted alkene R2C=CHR’ | Medium | |
| 665–730 | C=C bending Disubstituted cis alkene cis RCH=CHR’ | Strong | |
| Substituted Derivates of Benzene | 730–770 and 690–710 | C-H bending Monosubstituted benzene ring | Strong |
| 735–770 | C-H bending Ortho-disubstituted | Strong | |
| 750–810 and 680–730 | C-H bending Meta-disubstituted | Strong | |
| 790–840 | C-H bending Para-disubstituted | Strong |
IR Spectrum Exercises
After taking note of these values, put your knowledge to the test using Cheminfo’s interactive IR exercises
IR spectrum analysis can be a little intimidating at the beginning, but remember, the more you practice, the easier it becomes