The NH stretches of amines are in the region 3300-3000 cm-1. These bands are weaker and sharper than those of the alcohol OH stretches which appear in the same region. In primary amines (RNH2), there are two bands in this region, the asymmetrical NH stretch and the symmetrical NH stretch.
Secondary amines (R2NH) show only a single weak band in the 3300-3000 cm-1 region, since they have only one NH bond. Tertiary amines (R3N) do not show any band in this region since they do not have an NH bond.
(A shoulder band usually appears on the lower wavenumber side in primary and secondary liquid amines arising from the overtone of the NH bending band: this can confuse interpretation. Note the spectrum of aniline, below.)
The NH bending vibration of primary amines is observed in the region 1650-1580 cm-1. Usually, secondary amines do not show a band in this region and tertiary amines never show a band in this region. (This band can be very sharp and close enough to the carbonyl region to cause students to interpret it as a carbonyl band.)
Another band attributed to amines is observed in the region 910-665 cm-1. This strong, broad band is due to NH wag and observed only for primary and secondary amines.
The CN stretching vibration of aliphatic amines is observed as medium or weak bands in the region 1250-1020 cm-1. In aromatic amines, the band is usually strong and in the region 1335-1250 cm-1.
The spectrum of diethylamine is below. Note that this secondary amine shows only one NH stretch (3288). The CN stretch is at 1143, in the range for non-aromatic amines (1250-1020). Diethylamine also shows an NH wag (733).
Triethylamine is a tertiary amine and does not have an NH stretch, nor an NH wag. The CN stretch is at 1214 cm-1 (non-aromatic).