Spectra and structure of small ring compounds. XXXVI. 1-methylcyclopentene and 1,2-dimethylcyclopentene

Abstract

The i.r. spectra of solid and gaseous 1-methylcyclopentene and 1,2-dimethylcyclopentene were recorded from 4000 to 33 cm −1. The corresponding Raman spectra of the gases and liquids were measured. The fundamental vibrations of each compound have been assigned on the basis of group frequency correlations, band intensities, band contours and Raman depolarization values. The barrier hindering internal rotation of the methyl group has been calculated to be 1.93 kcal/mol for 1-methylcyclopentene. In 1,2-dimethylcyclopentene the methyl barrier is 1.77 kcal/mol for the B 2 vibrational mode.