Table of IR Absorptions

Functional Group Characteristic Absorption(s) (cm-1) Notes
Alkyl C-H Stretch2950 - 2850 (m or s) Alkane C-H bonds are fairly ubiquitous and therefore usually less useful in determining structure.
Alkenyl C-H Stretch
Alkenyl C=C Stretch
3100 - 3010 (m)
1680 - 1620 (v)
Absorption peaks above 3000 cm-1 are frequently diagnostic of unsaturation
Alkynyl C-H Stretch
Alkynyl C=C Stretch
~3300 (s)
2260 - 2100 (v)
Aromatic C-H Stretch
Aromatic C-H Bending
Aromatic C=C Bending
~3030 (v)
860 - 680 (s)
1700 - 1500 (m,m)
Alcohol/Phenol O-H Stretch 3550 - 3200 (broad, s) See "Free vs. Hyrdogen-Bonded Hydroxyl Groups" in the Introduction to IR Spectra for more information
Carboxylic Acid O-H Stretch 3000 - 2500 (broad, v)
Amine N-H Stretch 3500 - 3300 (m) Primary amines produce two N-H stretch absorptions, secondary amides only one, and tetriary none.
Nitrile C=N Stretch 2260 - 2220 (m)
Aldehyde C=O Stretch
Ketone C=O Stretch
Ester C=O Stretch
Carboxylic Acid C=O Stretch
Amide C=O Stretch
1740 - 1690 (s)
1750 - 1680 (s)
1750 - 1735 (s)
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) As with amines, an amide produces zero to two N-H absorptions depending on its type.

All figures are for the typical case only -- signal positions and intensities may vary depending on the particular bond environment.

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