Vibrational Spectra and Assignments for Series of Mono- and Dihalonaphthalenes

Abstract

Infrared and Raman spectra have been measured, and a complete vibrational assignment has been made for the following molecules: α-C₁₀H₇X and β-C₁₀H₇X where X = F, Cl, Br and I, 2,3-dibromonaphthalene, 2,3-dichloroquinoxaline, 1,4-dichloronaphthalene, and 1,4-dibromonaphthalene. The very low energy in-plane and out-of-plane halogen bending modes for these molecules were identified and assigned based on a comparison and correlation of halogen mass effect, band shapes and intensities, infrared and Raman selection rules, and Raman depolarization data. These vibrations were found to be relatively free from coupling with other vibrational modes of the molecule. The halogen stretching modes, on the other hand, were found to be strongly coupled with naphthalene skeletal modes to the extent that in several compounds no predominant halogen stretching mode could be identified. In several instances, supporting evidence is given which favors a particular assignment of a disputed vibrational assignment in naphthalene.