Influence of the hydrogen bond on the N-H stretching frequencies in amino-acids

Abstract

The spectra of glycine, its addition compounds and other amino-acids exhibit Raman lines in the region from 3250 cm^-1 to 2500 cm^-1 It has been shown that these lines cannot be assigned to N-H...O stretching vibrations, where the N atom has the covalency of three, but to N⁺-H...O stretching vibration where the N atom has the covalency of four. Using the data obtained with triglycine sulphate which has the largest number of N⁺-H...O bonds and whose H bond lengths are known, the correlation curve giving the relation between the N⁺-H...O stretching frequencies and the corresponding H bond lengths has been drawn. Using this correlation curve, the N⁺-H...O stretching frequencies appearing in α-glycine, γ -glycine, diglycine hydrochloride, diglycine hydrobromide, l-asparagine monohydrate and dl-alanine have been satisfactorily accounted for on the basis of the known hydrogen bond lengths in these substances.