IR

Typical Infrared Absorption Frequencies
	Stretching Vibrations			Bending Vibrations
Functional Class	Range (cm^-1)	Intensity	Assignment	Range (cm^-1)	Intensity	Assignment
Alkanes	2850-3000	Strong	CH₃, CH₂ & CH 2 or 3 bands	1350-1470 1370-1390 720-725	medium medium weak	CH₂& CH₃deformation CH₃ deformation CH₂ rocking
Alkenes	3020-3100 1630-1680 1900-2000	medium variable strong	=C-H & =CH₂ (usually sharp) C=C (symmetry reduces intensity) C=C asymmetric stretch	880-995 780-850 675-730	strong medium medium	=C-H & =CH₂ (out-of-plane bending) cis-RCH=CHR
Alkynes	3300 2100-2250	strong variable	C-H (usually sharp) C≡C (symmetry reduces intensity)	600-700	strong	C-H deformation
Arenes	3030 1600 & 1500	variable medium-weak	C-H (may be several bands) C=C (in ring) (2 bands) (3 if conjugated)	690-900	strong-medium	C-H bending & ring puckering
Alcohols & Phenols	3580-3650 3200-3550 970-1250	variable strong strong	O-H (free), usually sharp O-H (H-bonded), usually broad C-O	1330-1430 650-770	medium variable-weak	O-H bending (in-plane) O-H bend (out-of-plane)
Amines	3400-3500 (dil. soln.) 3300-3400 (dil. soln.) 1000-1250	weak weak medium	N-H (1°-amines), 2 bands N-H (2°-amines) C-N	1550-1650 660-900	medium-strong variable	NH₂ scissoring (1°-amines) NH₂ & N-H wagging (shifts on H-bonding)
Aldehydes & Ketones	2690-2840(2 bands) 1720-1740 1710-1720 1690 1675 1745 1780	medium strong strong strong strong strong strong	C-H (aldehyde C-H) C=O (saturated aldehyde) C=O (saturated ketone) aryl ketone a, ß-unsaturation cyclopentanone cyclobutanone	1350-1360 1400-1450 1100	str str med	a-CH₃ bending a-CH₂ bending C-C-C bending
Carboxylic acids and Derivatives	2500-3300 (acids) overlap C-H 1705-1720 (acids) 1210-1320(acids) 1785-1815 ( acyl halides) 1750 & 1820 (anhydrides) 1040-1100 1735-1750 (esters) 1000-1300 1630-1695(amides)	strong strong medium-strong strong strong strong strong strong strong	O-H (very broad) C=O (H-bonded) O-C (sometimes 2-peaks) C=O C=O (2-bands) O-C C=O O-C (2-bands) C=O (amide I band)	1395-1440 1590-1650 1500-1560	med med med	C-O-H bending N-H (1¡-amide) II band N-H (2¡-amide) II band
Nitriles Isocyanates, Isothiocyanates, Diimides, Azides & Ketenes	2240-2260 2100-2270	med med	C≡N (sharp) -N=C=O, -N=C=S -N=C=N-, -N₃ , C=C=O