Absolute raman intensities of the carbonyl stretching band in para substituted methyl benzoates

Article abstract of DOI:10.1002/bbpc.19890931206

The absolute Raman intensities of the v_C=0 band of para-substituted methyl benzoates have been measured in CCl₄ solution at different excitation frequencies. The intensities depend on a preresonance Raman effect (PRRE) and are correlated with theoretical expressions which describe the dispersion of the Raman intensity as a function of the excitation frequency and the experimental UV frequencies of the compounds, in particular the π→π^{* 1}L_a band. The Raman intensities free from PRRE are deduced by extrapolating the experimental values to a zero excitation frequency. These extrapolated intensities depend on the electron-donating character of the substituents and on the extent of the conjugated system. The depolarization ratio of the v_C=0 band in methyl benzoates increases with the excitation energies. This ratio is higher for the para-substituted derivatives.