Acetamide hemihydrochloride: a case of false high crystallographic symmetry. Vibrational spectra of the 2H0 and NN′O-2H5 derivatives

Abstract

The i.r. and Raman spectra of the title compounds have been examined. The i.r. spectrum remains highly anomalous after deuteriation. The centre of gravity of the very broad absorption due to hydroxy stretching is ca. 920 cm^–1 for both OH and OD compound. This constancy in frequency is incompatible with a symmetrical O ⋯ H ⋯ O bond, and shows that the centrosymmetry found for the (CH₃CONH₂)₂H⁺ complex by X-ray and neutron diffraction is not the true molecular symmetry. Several i.r.–Raman frequency coincidences are found. The stronger Raman bands of (CH₃CONH₂)₂H⁺ all have counterparts in the Raman spectrum of solid CH₃CONH₂; prominent frequencies of (CH₃CONH₂)₂H⁺ without good counterparts in CH₃CONH₂ have counterparts in the CH₃C(OH)N⁺H₂ spectrum, in agreement with structure (II) for the complex.