Assignment of vibrational spectra of halogenated naphtalenes and n-heterocycles

Analysis and prediction of vibrational spectra may be based upon similarities in vibrational modes of molecules whose vibrational spectra are understood. Frequently the molecule whose vibrational assignment is known is simpler than the molecule to be analyzed. The validity of this method lies in the similarities of the molecular vibrations between the simple and the more complex molecules. In molecules of high symmetry, infrared and Raman spectra are highly complementary. In molecules of lower symmetry, the information given by the two methods overlaps somewhat. Both types of spectra are employed in this work. Benzene and the halobenzenes comprise the model (known) system for the vibrational study in this work. Naphthalene and various halonaphthalenes belong to the system to be investigated. Naphthalene and its halogenated derivatives are a more complex system, in terms of molecular vibrations, than benzene and the halobenzenes. Therefore an analysis of this nature provides a test of our ability to accurately describe the vibrations of the benzene system, and whether these descriptions may logically be extended to other systems. In addition to the information furnished by the benzene-halobenzene system, many assignments are made on the basis of spectral data, including band shapes and intensities, depolarization of Raman bands, etc. Such spectral data is important in making a good correlation between naphthalene and the halonaphthalenes.