Vibration Spectra and Molecular Structures of n-Butyl Chloride and n-Butyl Bromide in Relation to Parallel (1:3) Interactions

The vibration spectra of liquid n-butyl chloride and n-butyl bromide are observed in the region of 1500–100 cm−1. From the analyses of spectra corresponding to the skeletal deformation vibrations, the molecular configurations are determined for both molecules. All the possible rotational isomers, the TT, GT, TG, GG, and GG′ forms, are observed for n-butyl chloride, while four isomers, the TT, GT, TG, and GG forms, are observed for n-butyl bromide. The results are compared with those of the electron-diffraction methods. It is shown that unfamiliar interactions must be considered for the parallel (1:3) interaction between methyl and chlorine substituents.