THE N-H STRETCHING VIBRATION BAND IN SEVERAL AROMATIC COMPOUNDS

Abstract

Theoretical work recently reported on pyrrole, indole, carbazole, aniline, and diphenyl amine has included a calculation of the electron density on the nitrogen atoms of each of these $compounds^{1}$. In order to see if these calculated values could be checked by infrared means, a detailed investigation of the absorption bands attributed to the N-H stretching vibrations has been undertaken. A lithium fluoride prism spectrometer was employed, each of these compounds being studied over a wide range of concentration and cell length. This study has resulted in a clarification of contradictory reports on hydrogen bonding made by previous $workers.^{2}$ Evidence will be presented for concluding that in pyrrole the unassociated band is simple, thus removing the experimental basis for Pauling's theory of two types of $pyrrole.^{3}$ A discussion will be included of the absolute values of the unassociated N-H vibration frequencies and their relation with the calculated electron densities of the nitrogen atoms in the corresponding molecules.