Ochem IR Spectroscopy

Aromatic C-C

Two peaks usually in the range of 1500−1600 cm⁻¹

C=C

~1650 cm⁻¹

C=O

~1710 cm⁻¹

C=O (ester)

~1735 cm⁻¹

C≡C

~2100-2300 cm⁻¹

C≡N

~2100-2300 cm⁻¹

C-H (aldehyde)

Two peaks at 2710 cm⁻¹ and 2810 cm⁻¹

sp³ C-H

Just to the right of 3000 cm⁻¹

sp² C-H

Just to the left of 3000 cm⁻¹

sp C-H

~3300 cm⁻¹

N-H

~3300 cm⁻¹ (one peak for −NH, two peaks for −NH₂)

O-H (alcohol)

~3400 cm⁻¹ (a broad, smooth peak)

O-H (acid)

~2500−3500 cm⁻¹ (a very broad, ugly peak, not smooth)

Fingerprint region

0−1400 cm⁻¹, unreliable so ignore, contains C-C, C-O and C-N

OH

3200-3600, strong broad, and C-O around 1000-1300

COOH

2500-3500 OH, and 1700 Carbonyl

NH2

3100-3500, double peak

RNH

3100-3500, single peak

CN

2250

CONH2

3100-3500 double peak NH2, Carbonyl at 1650ish, and C-N at 1000-1300

Benzene

1500 and 1600 C--C, CH 3050

Monosub benzene

690 and 750

O-sub

735

Meta-sub

690 and 780

p-sub

820

Aldehyde

Carbonyl around 1700, and CH around 2700

Ketone

Carbonyl at 1700

Ester

Carbonyl at 1700, C-O around 1000

Ether

C-O around 1000

Terminal Alkynes

---C-H 3300, C---C at 2080-2280, H-C---C-R 600-700

Internal Alkynes

C---C 2080-2280, C-H around 2850 and 2960

Alkenes

C-H around 3100

Alkanes

C-H around 2950/3000

NO2

1350 and 1530 Fangs