Compounds Containing –NH 2, –NHR, and –NR 2 Groups

This chapter discusses the characteristic infrared (IR) and Raman frequencies of —NH 2 , —NHR, and —NR 2 containing compounds. The compounds that contains the —NH 2 , —NHR, and —NR 2 moieties include aliphatic amines, aromatic amines, heterocychc aromatic compounds, amides, thioamides, ammonium, salts, hydroxylamines, and hydrazines. Most of the open-chain amides and cyclic amides with a ring size larger than eight atoms exist as trans isomers, while the cyclic amides with a ring size of less than eight atoms exist as cis isomers. In dilute solution, the NH stretch band of the trans species occurs at frequency higher than the corresponding cis isomer. The C—N—H bending vibration in C 2 NH groups changes the CNH angle. Secondary aromatic amines sometimes show an extra IR band about 1510 cm −1 near to the 1500 cm −1 aromatic ring band involving CNH bending. Secondary amines and arylamines exhibit only a single characteristic IR and Raman band in the N—H stretching region (3500–3100 cm- 1 ). However, the secondary amides present additional characteristic IR bands in this region such as the 1550 cm −1 overtone band near 3100 cm −1 .