RAMAN AND INFRARED SPECTRA, CONFORMATIONAL STABILITY, BARRIERS TO INTERNAL ROTATION, AND AB INITIO CALCULATIONS OF CROTYL CHLORIDE AND CROTYL BROMIDE

Abstract

The infrared (3200 to $40 cm^{-1}$) and Raman (3500 tp $10 cm^{-1}$) spectra have been recorded for the fluid and solid phases of crotyl chloride and crotyl bromide. These data have been interpreted on the basis that the gauche form (two double bonds oriented gauche to one another) is the most stable form in the fluid phases and the only form remaining in the solid state. The asymmetric torsional fundamental of the more stable gauche and the higher energy cis form have been observed in the far infrared spectrum of the gas. From these data the asymmetric potential function governing the internal rotation about the C-C bond has been determined. Similarly, the potential function governing the internal rotation of the $CH_{3}$ group has also been determined from the far infrared spectrum of the gas. A complete vibrational assignment is proposed. These data are compared to the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing the 3-21G* and 6-31G* basis sets. These results are compared to the corresponding quantities for some similar molecules.