Infrared of nitro compounds

Nitro compounds show two strong bands, one near 1550 and one near 1350, these may overlap with the aromatic region, but are usually easy to see.

1-nitrohexane

Nitrobenzene

Aliphatic nitro compounds have the lower-frequency NO₂ band absorb with less intensity. Aromatic nitro compound have both absorptions at equal intensity.

Conjugation (such as being aromatic) shifts both bands to lower frequencies.

The nitroso group (R-N=O) gives only one strong band at 1600-1500.