IR Spectroscopy Numbers

C–C single-bond absorption?

~1400 cm⁻¹

Isolated alkene C=C absorption?

1640–1680 cm⁻¹; usually weak to medium

Conjugated alkene C=C absorption?

1620–1640 cm⁻¹

Aromatic C=C absorption?

~1600 cm⁻¹

Alkyne C≡C absorption?

2100–2200 cm⁻¹; often weak for internal alkynes

sp³ C–H absorption?

2800–3000 cm⁻¹

sp² C–H absorption?

3000–3100 cm⁻¹

sp C–H absorption?

~3300 cm⁻¹; terminal alkynes

Alcohol O–H absorption?

~3300 cm⁻¹; broad

Carboxylic acid O–H absorption?

2500–3500 cm⁻¹; extremely broad

Amine N–H absorption?

~3300 cm⁻¹; broad, spiked

Alcohol C–O absorption?

1000–1200 cm⁻¹; not unique to alcohols

Typical carbonyl C=O absorption?

~1700 cm⁻¹; strong

Amide C=O absorption?

1640–1680 cm⁻¹; strong

Carboxylic acid or ester C–O absorption?

1000–1300 cm⁻¹

Aldehyde C–H absorption?

2700–2800 cm⁻¹; absent in ketones

C–N single-bond absorption?

~1200 cm⁻¹

Imine C=N absorption?

~1660 cm⁻¹; intense

Nitrile C≡N absorption?

2200–2260 cm⁻¹; typically intense

Fingerprint region?

600–1400 cm⁻¹; complex, molecule-specific peaks