THE VINYL TORSION IN SOME SUBSTITUTED STYRENES

Abstract

The low frequency torsional overtone ($\Delta\nu = 2$) of the vinyl group has been observed in the gas phase Raman spectra of m- and p-chlorostyrene, m- and p-fluorostyrene and p-methylstyrene. The calculated barriers to internal rotation are all slightly smaller than for styrene itself. It appears that the conventional resonance and induction arguments used in explaining the reactions of para-substituted aromatics play no role in the ground electronic states of these molecules. The slight downward trend in the barriers may he explained in terms of a small increase in non-dominant steric forces.