Infrared, ultraviolet, and nuclear magnetic resonance spectra (at room temperature and at low temperatures), solvent effects, and substituent effects have been used to show that the double carbonyl peaks of the N-nitrocarbamates stem from rotational isomerism involving the carboxyl groups, and not from Fermi resonance. Cyclic nitrocarbamates in which this type of rotation is impossible have only a single carbonyl band in the infrared. The rotation ...
