Table 1. Characteristic Infrared Absorption Peaks

Type of Stretch		Frequency (cm^-1)	Strength/Other Information
O – H	alcohol	3300	Strong Broad, rounded when hydrogen bonded Sharp in the absence of hydrogen bonding
	acid	2500-3500	Very broad
N – H	Amine or amide	3300	Weak/moderate 2 spikes for 1^o 1 spike for 2^o Absent for 3^o
N – H bend	1^O Amine	1560 – 1640	Broad (usually weak to moderate)
C – H	sp C – H	3300	Variable
	sp^2 C – H	> 3000	Variable
	sp^3 C – H	< 3000	Variable
	Aldehyde C – H	~2700 AND ~2800	weak/moderate
C Ξ C		< 2200	absent/weak/mod
C Ξ N		> 2200	mod/strong
C = O	Ester	1730 – 1740	Strong
	Strained cyclic ketone	1740 - 1815	Stong
	Ketone	~1710	Strong
	Aldehyde	~1710	Strong
	Acid	~1710	Strong
	Amide	1640 – 1680	Strong
Note: Conjugation generally shifts a carbonyl ~10-30 cm^-1 lower in frequency.
C = C	Isolated	1640 – 1680	weak/mod
	Conjugated	1620-1640	weak/mod
	Aromatic	~1600 (May also see peaks at about 1580, 1500, and 1450)	weak/mod
C – O	ester	1000-1300	Strong