Torsional isomerism of allyl chloride, bromide and iodide

Abstract

The infra-red spectra of allyl (propene-3) chloride, bromide and iodide vapour and liquid have been examined from 60 to 2000 cm^–1, and crystal from 60 to 450 cm^–1. Raman polarizabilities have been measured for liquid allyl chloride and bromide. The predominating torsional isomer is a twisted-trans form, the proportion of the minor cis form decreasing from chloride to iodide. The structures observed support the view that spin correlation plays an important role in torsion barriers.