Hydrogen bond formations between pyrazine and formic acid and between pyrazine and trichloroacetic acid

The hydrogen bond formations between pyrazine and formic acids and between pyrazine and trichloroacetic acids were studied through observation of the Raman and infrared spectra for mixture of pyrazine and formic acid and also mixture of pyrazine and trichloroacetic acid at 77 K. It was observed that the mutual exclusion principle held for the Raman and infrared spectra of both mixtures, even for the spectra of the samples whose mixing mole ratio of acids was very low. This fact clearly indicates that the hydrogen bonded molecule does not exist in the form of formic acid–pyrazine or trichloroacetic acid–pyrazine whose geometry belongs to the Cs point group, but exists in the form of formic acid–pyrazine–formic acid or trichloroacetic acid–pyrazine–trichloroacetic acid belonging to the Ci point group.

Graphical abstract(a) Formic acid–pyrazine–formic acid, (b) trichloroaceticacid–pyrazine–trichloroaceticacid.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Raman and infrared spectra of the mixture of pyrazine and formic acid were observed. ► Spectra of the mixture of pyrazine and trichloroacetic acid were also observed. ► Hydrogen bonded molecules exist in the form of acid–pyrazine–acid.