IR Stretching Frequencies of Common Functional Groups

Question 1

O-H stretch

Answer 1

3300/cm (broad)

Question 2

N-H stretch (secondary amine)

Answer 2

3300/cm (broad w/ one spike)

Question 3

N-H stretch (primary amine)

Answer 3

3300/cm (broad w/ 2 spikes)

Question 4

C-H stretch (sp hybrid)

Answer 4

3300/cm (sharp)

Question 5

C-H stretch (sp2 hybrid)

Answer 5

Just above 3000/cm (sharp)

Question 6

O-H stretch (carboxylic acids)

Answer 6

3500-2500/cm (very broad and maximizes at 3000/cm)

Question 7

C-H stretch (sp3)

Answer 7

Just below 3000/cm (relatively sharp w/ some structure)

Question 8

C-H stretch (aldehyde)

Answer 8

Sharp doublet at 2800/cm and 2700/cm

Question 9

C=-C (triple bond) stretch

Answer 9

2200/cm (sharp) for terminal triple bonds, but will be absent for triple bonds that are symmetrical

Question 10

C=-N (triple bond) stretch (cyano group)

Answer 10

2200/cm (sharp and strong)

Question 11

C=O stretch (Carbonyl group)

Answer 11

1710/cm (sharp and strong) can be shifted to the left by ring strain and to the right by conjugation

Question 12

C=N stretch

Answer 12

1680/cm to 1640/cm

Question 13

C=C stretch (isolated double bond)

Answer 13

1680/cm to 1640/cm

Question 14

C=C stretch (conjugated double bond)

Answer 14

1640/cm to 1620/cm

Question 15

C=C stretch (benzene)

Answer 15

1600/cm

Question 16

Fingerprint Region

Answer 16

Anything below 1500/cm