Table of IR Absorptions Functional Group Alkyl C-H Stretch Alkenyl C-H Stretch Alkenyl C=C Stretch Alkynyl C-H Stretch Alkynyl C=C Stretch Aromatic C-H Stretch Aromatic C-H Bending Aromatic C=C Bending Alcohol/Phenol O-H Stretch Carboxylic Acid O-H Stretch Amine N-H Stretch Nitrile C=N Stretch Aldehyde C=O Stretch Ketone C=O Stretch Ester C=O Stretch Carboxylic Acid C=O Stretch Amide C=O Stretch Amide N-H Stretch Characteristic Absorption(s)(cm-1)

Notes

Alkane C-H bonds are fairly ubiquitous and 2950 - 2850 (m or s) therefore usually less useful in determining structure. 3100 - 3010 (m) 1680 - 1620 (v) Absorption peaks above 3000 cm-1 are frequently diagnostic of unsaturation

~3300 (s) 2260 - 2100 (v)

~3030 (v) 860 - 680 (s) 1700 - 1500 (m,m)

3550 - 3200 (broad, s) 3000 - 2500 (broad, v) 3500 - 3300 (m)

See "Free vs. Hyrdogen-Bonded Hydroxyl Groups" in the Introduction to IR Spectra for more information

Primary amines produce two N-H stretch absorptions, secondary amides only one, and tetriary none.

2260 - 2220 (m)

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.

3700 - 3500 (m)

As with amines, an amide produces zero to two NH absorptions depending on its type.