IR Spectroscopy by Functional Group
Alkanes
Indentification of absorbance Wavenumbers, cm-1
sp3 C-H stretch 2960-2850 (<3000)
Alkenes
sp2 C-H stretch 3100-3020 cm-1 (>3000)
C=C stretch 1680-1620 cm-1 (often weak)
Alkynes
sp C-H stretch 3333-3267 cm-1
C-C triple bond stretch 2260-2100 cm-1 (often weak)
Nitriles
C-N triple bond stretch 2260-2240 cm-1 (aliphatic)
2240-2222 cm-1 (conjugated)
Alcohols
O-H stretch 3600-3200 cm-1 (strong and broad)
C-O stretch 1150-1050 cm-1
Aromatic Compounds
sp2 C-H stretch 3100-3020 cm-1 (>3000)
C=C stretch ~ 1585 cm-1
Aromatic overtones of ring bends 2000-1667 cm-1
Aromatic out-of-plane ring bends ~ 900-700 cm-1 (see p. 519)
Amines
N-H stretch 3500-3350 cm-1
C-N stretch (often weak and hard to find) 1250-1020 cm-1 (aliphatic)
1342-1266 cm-1 (aromatic)
Aldehydes
C-H stretch of -CHO 2830-2695 cm-1
C=O stretch 1740-1720 cm-1
Ketones
C=O stretch 1750-1710 cm-1 (1715 is typical for aliphatic ketones)
1685-1665 cm-1 (conjugated)
Carboxylic acids
O-H of –CO2H 3600-2500 cm-1 (centered at ~ 3000)
C=O stretch 1720-1710 cm-1 (aliphatic), 1700-1680 cm-1 (conjugated)
Esters
C=O stretch 1750-1735 cm-1 (aliphatic), 1720-1715 cm-1 (conjugated)
C-O stretch 1300-1000 cm-1