Table 1: Principal IR Absorptions for Certain Functional Groups above 1400 cm-1


Functional Group Names
&
Example Compounds

Absorption Ranges Frequency (cm--1) [Look for a single absorption in these regions unless stated otherwise.]


Type of Vibration
(causing IR absorption)

Alkanes:


3000-2800
(Note: The absorptions can be seen a several distinct peaks in this region.)

1500-1450


C-H Stretch

 

C-H Bend

Alkenes:


3100-3000

1675-1600


=C-H Stretch

C=C Stretch

Alkynes:


3300-3200

2200-2100


Aromatic Rings:


3100-3000

1600-1580

1500-1450


=C-H Stretch

C=C Stretch

C=C Stretch

Alcohols, Phenols:


3600-3100
(Note: Phenols MUST have Aromatic Ring Absorptions too.)


(1300-1000)


H-bonded O-H Stretch




(C - O Stretch)

Nitriles:

2300-2200

Ketones:

1750-1625

C=O Stretch

Table 1 Continued: Principal IR Absorptions for Certain Functional Groups above 1400 cm-1

Aldehydes:


1750-1625

2850-2800

2750-2700


C=O Stretch

C-H Stretch off C=O

C-H Stretch off C=O

Carboxylic Acids:


3400-2400
(Note: This peak always covers the entire region with a VERY BROAD peak.)

1730-1660


H-bonded O-H Stretch




C=O Stretch

Ethers:


(1300-1000)


(C - O Stretch)

Esters:


1735

(1300-1000)


C=O Stretch

(C - O Stretch)

Amines: Primary


3500-3200
(TWO PEAKS!)

1640-1560


N-H Stretch


N-H Bend

Amines: Secondary

3500-3200
(ONE PEAK!)

1550-1450


N-H Stretch


N-H Bend
Nitro Groups:


(Note: Both peaks are < 200 cm-1 apart.)

1600-1500

1400-1300

N=O Stretch

N=O Stretch

Amides:

3500-3100

1670-1600

1640-1550

N-H Stretch

C=O Stretch

N-H Bend