Some structural problems and the vibration spectra of a series of N-substituted ethylenimines

On a basis of comparison of Raman and IR absorption spectra, as well as measurements of intensities and degrees of depolarization of Raman lines, pulsation (breathing) vibrations of the ethylenimine ring -_sNin a series of N-substituted ethylenimines are identified. Alkyl substituents increase_sNas compared with ethylenimine, probably because of change in the hydridization of the electron clouds of the nitrogen due to steric causes. The high values of_sNfor substituents capable of conjugation effects, is in accord with the hypothesis that the lone electron pair of the nitrogen participates in conjugation. Furthermore, when N enters into the composition of a 3-membered ring, the lone pair exhibits diminished capacity for delocalization. The intensity of the Raman line_sN of N-phenylethylenimine is anomalously high, and the cause of this requires explaining. UV spectra are given.