Raman Spectra of Amino Acids and Related Compounds V. Deuterium Substitution in the Amino Group

Abstract

Raman Spectra are reported for CH3·ND2, CH3·ND3+, +D3N·ND3+ and +D3N·ND2. Comparison with the spectra of the corresponding compounds containing no deuterium reveals three classes of frequencies: (1) Those arising from the methyl group are unchanged within the experimental error by deuterium substitution in the amino group. (2) The amino and ammonium group frequencies are higher in the H than in the D compounds by a factor of 1.33 to 1.36. Among these a characteristic —ND3+ valence vibration is found near 2180 cm—1, corresponding to an —NH3+ vibration near 2970. These frequencies are broad and rather faint, and are lower by several hundred wave numbers than the corresponding sharp intense lines arising from the uncharged —NH2 and —ND2 groups. The principal deformation frequency of the NH3+ and NH2 groups appear to be near 1620; the corresponding frequency of the —ND3+ and —ND2 groups is near 1200. (3) Other frequencies are changed by a factor of less than 1.3 when deuterium is substituted for hydrogen in the nitrogen. The most intense lines in this group are the C–N and N–N stretching frequencies near 1000 cm—1, which show a decrease of 20 to 50 cm—1 on deuterium substitution. Some calculations, based on a very simple model, were made for these frequencies, but they did not quantitatively explain the observed results.