Ab initio analysis of C-H and C-C stretching intensities in Raman spectra of hydrocarbons

Abstract

Molecular polarizability and changes in the polarizability associated with the stretch of C–C and C–H bonds have been calculated for thirty-four saturated hydrocarbons, including the series of n-alkanes to C15, as well as several cyclo- and bicycloalkanes, propellanes, prismanes, and hedranes. The ab initio results (HF/D95(d,p)) are compared to experimental Raman trace scattering intensities where such information is available. Possible factors governing trends in the magnitude of the derivatives are considered. For the C–C stretches, chain length and position along the chain are the most important factors for the n-alkanes, whereas strain appears to be significant for the ring and caged structures. For the C–H stretches, the most significant factors are the same as those found in our earlier work: location, type, and orientation relative to the carbon skeleton.Key words: hydrocarbons, Raman scattering intensities, molecular polarizability, polarizability derivatives, theory of atoms in molecules.