Non-NMR Spectroscopies Solutions: #11

11.* (1992 2 3) Nylon is a typical polyamide. How could nylon be spectroscopically distinguished from polystyrene?

Nylon is a polyamide, so it contains many amide groups. Polystyrene, on the other hand, is a polymer which contains aromatic ring structures. IR spectroscopy could be used to distinguish the two. IR is good for insoluble samples; in fact it requires that no water be present (the O-H stretches in water distort the spectrum of the sample.) More specifically, nylons would show an amide C=O stretch at about 1690 cm-1 as well as an N-H stretch in the form of a sharp peak above 3000 cm-1. Polystyrene would show an aromatic C-H stretch (multiple short peaks above 3000 cm-1) as well as aromatic C-C stretching modes, which are complex peaks found in the region of 900-1100 cm-1.