Vibrations of pyrrole, N-substituted pyrroles, and their cations

The vibrations of pyrrole, N-deuteropyrrole, N-fluoropyrrole, N-aminopyrrole and N-methylpyrrole are studied. The evolution of the vibrational wavenumbers of pyrrole is examined, as the mass of the nitrogen-bonded hydrogen atom is artificially increased. It is found that some vibrations are very sensitive to the mass of the substituent bonded to the nitrogen, and this can be viewed as vibrations mixing as that mass increases; however, these mixings stablilize by the time a mass of 14 mu is reached. A consistent numbering scheme for the ring-localized vibrations of N-substituted pyrroles is then put forward. A discussion of the vibrations of the cations of pyrrole and N-substituted pyrroles is then presented. Calculated vibrational wavenumbers are compared to experimental ones for pyrrole, N-deuteropyrrole and N-methylpyrrole, as well as the pyrrole cation. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

The vibrations of pyrrole and its various derivatives were studied, revealing that some vibrations are highly sensitive to the mass of the substituent, with mixings stabilizing at a mass of 14 mu. A consistent numbering scheme was proposed, and calculated vibrational wavenumbers were compared to experimental results.