The N[Single Bond]H Harmonic Bands of Pyrrole at lambda9900, and the Structure of the Pyrrole Molecule

In their study of the infra-red absorption of organic substances in carbon tetrachloride solution Wulf and Liddell (1) found that the strong second harmonic N-H band of pyrrole is accompanied by a weak satellite which lies approximately 50 cm^-1 to the long wave side and has roughly one-twentieth the intensity of the main band. The main band has been attributed by Pauling (2) to a planar pyrrole molecule and the weak satellite to a second molecular species in which the imino hydrogen lies out of the plane of the other atoms.