Vibrational spectra and structure of small ring compounds chlorocyclopentane and bromocyclopentane

Abstract

The infrared and Raman spectra of chlorocyclopentane, bromocyclopentane, and α-bromocyclopentane- d 1 were recorded and the fundamentals assigned. A temperature study of the Raman effect of chlorocyclopentane indicated that at least two distinct isomers were present. The presence of at least two conformers coupled with a very high frequency of the A′ ring puckering fundamental, 188 cm −1, indicates that the barrier to pseudorotation is at least an order of magnitude greater than originally proposed. Neither the frequency of the A′ ring puckering mode nor the presence of conformers was observed in either of the bromocyclopentanes investigated, but it is believed that the magnitude of the barrier is probably similar to that predicted for the chloride. Vibrational assignments are proposed for these molecules.