Absolute Raman Intensities of the Carbonyl Stretching Band in Para Substituted Methyl Benzoates

Abstract

The absolute Raman intensities of the vc=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*1La 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 νc=0 band in methyl benzoates increases with the excitation energies, this ratio is higher for the para substituted derivatives.