Circular Dichroism of an Optically Active Olefin Chromophore: (R)-3-Methylcyclopentene

The electronic circular dichroism and absorption spectra of (R)-3-methylcyclopentene have been measured in the gas phase down to 1400 Á. Four distinct bands with alternating sign are observed in the circular dichroism spectrum. Ab initio self-consistent field wave functions obtained for the ground and excited states of (R)-3-methylcyclopentene are used to calculate the optical rotational strengths of the lowest lying electronic excited states. The assignment of the measured spectra, based on the results of the calculations, shows that the first three observed bands can be identified with π→π and π→Rydberg (R) type excitations of the olefin chromophore and σ-R transitions of the skeletal frame. The first band is probably a combination of π→R and σ→R transitions.