Characteristic IR Band Positions

Characteristic IR Band Positions

Group				Frequency Range (cm-1)
OH stretching vibrations
Free OH				3610-3645 (sharp)
Intramolecular H bonds				3450-3600 (sharp)
Intermolecular H Bonds				3200-3550 (broad)
Chelate Compounds				2500-3200 (very broad)
NH Stretching vibrations
Free NH				3300-3500
H bonded NH				3070-3350
CH Stretching vibrations
=-C-H				3280-3340
=C-H				3000-3100
C-CH3				2862-2882, 2652-2972
O-CH3				2815-2832
N-CH3 (aromatic)				2810-2820
N-CH3 (aliphatic)				2780-2805
CH2				2843-2863,2916-2936
CH				2880-2900
SH Stretching Vibrations
Free SH				2550-2600
C=-N Stretching Vibrations
Nonconjugated				2240-2260
Conjugated				2215-2240
C=-C Stretching Vibrations
C=-CH (terminal)				2100-2140
C-C=-C-C				2190-2260
C-C=-C-C=-CH				2040-2200
C=O Stretching Vibrations
Nonconjugated				1700-1900
Conjugated				1590-1750
Amides				~1650
C=C Sretching Vibrations
Nonconjugated				1620-1680
Conjugated				1585-1625
CH Bending Vibrations
CH2				1405-1465
CH3				1355-1395, 1430-1470
C-O-C Vibrations in Esters
Formates				~1175
Acetates				~1240, 1010-1040
Benzoates				~1275
C-OH Stretching Vibrations
Secondary Cyclic Alcohols				990-1060
CH out-of-plane bending vibrations    in substituted ethylenic systems
-CH=CH2				905-915, 985-995
-CH=CH-(cis)				650-750
-CH=CH-(trans)				960-970
C=CH2				885-895
Characteristic IR Absorption Frequencies of Organic Functional Groups
Functional Group		Type of Vibration	Characteristic Absorptions (cm-1)		Intensity
Alcohol
O-H		(stretch, H-bonded)	3200-3600		strong, broad
O-H		(stretch, free)	3500-3700		strong, sharp
C-O		(stretch)	1050-1150		strong
Alkane
C-H		stretch	2850-3000		strong
-C-H		bending	1350-1480		variable
Alkene
=C-H		stretch	3010-3100		medium
=C-H		bending	675-1000		strong
C=C		stretch	1620-1680		variable
Alkyl Halide
C-F		stretch	1000-1400		strong
C-Cl		stretch	600-800		strong
C-Br		stretch	500-600		strong
C-I		stretch	500		strong
Alkyne
C-H		stretch	3300		strong,sharp
		stretch	2100-2260		variable, not present in symmetrical alkynes
Amine
N-H		stretch	3300-3500		medium (primary amines have two bands; secondary have one band, often very weak)
C-N		stretch	1080-1360		medium-weak
N-H		bending	1600		medium
Aromatic
C-H		stretch	3000-3100		medium
C=C		stretch	1400-1600		medium-weak, multiple bands
Analysis of C-H out-of-plane bending can often distinguish substitution patterns
Carbonyl		Detailed Information on Carbonyl IR
C=O		stretch	1670-1820		strong
(conjugation moves absorptions to lower wave numbers)
Ether
C-O		stretch	1000-1300 (1070-1150)		strong
Nitrile
CN		stretch	2210-2260		medium
Nitro
N-O		stretch	1515-1560 & 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=O	stretch	1670-1820	strong
(conjugation moves absorptions to lower wave numbers)
Acid
C=O	stretch	1700-1725	strong
O-H	stretch	2500-3300	strong, very broad
C-O	stretch	1210-1320	strong
Aldehyde
C=O	stretch	1740-1720	strong
=C-H	stretch	2820-2850 & 2720-2750	medium, two peaks
Amide
C=O	stretch	1640-1690	strong
N-H	stretch	3100-3500	unsubstituted have two bands
N-H	bending	1550-1640
Anhydride
C=O	stretch	1800-1830 & 1740-1775	two bands
Ester
C=O	stretch	1735-1750	strong
C-O	stretch	1000-1300	two bands or more
Ketone
acyclic	stretch	1705-1725	strong
cyclic	stretch	3-membered - 1850 4-membered - 1780 5-membered - 1745 6-membered - 1715 7-membered - 1705	strong
,-unsaturated	stretch	1665-1685	strong
aryl ketone	stretch	1680-1700	strong

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