Characteristic IR Absorption Frequencies of Organic Functional Groups
Functional Group
Type of Vibration Characteristic Absorptions (cm-1) Intensity
Alcohol
O-H(stretch, H-bonded) 3200-3600strong, broad
O-H(stretch, free)3500-3700 strong, sharp
C-O(stretch)1050-1150 strong
Alkane
C-Hstretch2850-3000 strong
-C-Hbending1350-1480 variable
Alkene
=C-Hstretch3010-3100 medium
=C-Hbending675-1000 strong
C=Cstretch1620-1680 variable
Alkyl Halide
C-Fstretch1000-1400 strong
C-Clstretch600-800 strong
C-Brstretch500-600 strong
C-Istretch500 strong
Alkyne
C-Hstretch3300 strong,sharp
stretch 2100-2260variable, not present in symmetrical alkynes
Amine
N-Hstretch3300-3500 medium (primary amines have two bands; secondary have one band, often very weak)
C-Nstretch1080-1360 medium-weak
N-Hbending1600 medium
Aromatic
C-Hstretch3000-3100 medium
C=Cstretch1400-1600 medium-weak, multiple bands
Analysis of C-H out-of-plane bending can often distinguish substitution patterns
CarbonylDetailed Information on Carbonyl IR
C=Ostretch 1670-1820strong
(conjugation moves absorptions to lower wave numbers)
Ether
C-Ostretch1000-1300 (1070-1150) strong
Nitrile
CNstretch2210-2260 medium
Nitro
N-Ostretch1515-1560 & 1345-1385 strong, two bands


IR Absorption Frequencies of Functional Groups Containing a Carbonyl (C=O)
Functional Group
Type of Vibration Characteristic Absorptions (cm-1) Intensity
Carbonyl
C=Ostretch 1670-1820strong
(conjugation moves absorptions to lower wave numbers)
Acid
C=Ostretch 1700-1725strong
O-Hstretch 2500-3300strong, very broad
C-Ostretch 1210-1320strong
Aldehyde
C=Ostretch 1740-1720strong
=C-Hstretch 2820-2850 & 2720-2750medium, two peaks
Amide
C=Ostretch 1640-1690strong
N-Hstretch 3100-3500unsubstituted have two bands
N-Hbending 1550-1640
Anhydride
C=Ostretch 1800-1830 & 1740-1775two bands
Ester
C=Ostretch1735-1750 strong
C-Ostretch 1000-1300two bands or more
Ketone
acyclicstretch1705-1725 strong
cyclicstretch3-membered - 1850
4-membered - 1780
5-membered - 1745
6-membered - 1715
7-membered - 1705
strong
a,b-unsaturated stretch1665-1685strong
aryl ketonestretch 1680-1700strong



A good general reference for more detailed information on interpretation of infrared spectra (as well as other spectroscopic techniques) is Silverstein, R.M.; Bassler, G.C.; and Morrill, T.C. Spectrometric Identification of Organic Compounds. 4th ed. New York: John Wiley and Sons, 1981. QD272.S6 S55

A more complete listing of functional group absorption frequencies ma be found in: Nakanishi, Koji Infrared Absorption Spectroscopy. QD95.N383