Calculation of Raman intensities for the ring-puckering vibrations of cyclopentene and 2,5-dihydrofuran

Abstract

Raman intensities are calculated for the ring-puckering vibrations of cyclopentene and 2,5-dihydrofuran using an anisotropic atom–point dipole interaction model to calculate the elements of the molecular polarizability tensor. Large second-order terms are calculated for both molecules in the expansions of the molecular polarizability tensor elements in the ring-puckering coordinate [‖(∂2αμν/∂Z2)0‖≫0]. These terms result in intense calculated Δv = 2 overtone transitions, in agreement with experimental observations. The calculations predict that the Δv = 2 transitions of cyclopentene are one to two orders of magnitude more intense than the Δv = 1 fundamentals, while the two sets of transitions are comparable in intensity in 2,5-dihydrofuran. Although the shape of the band contours precludes observation of the Δv = 1 transitions for either molecule, the calculations suggest that the fundamental transitions of cyclopentene would not be observable even if the band shape were amenable to observation.