Intermolecular forces and solvent effects I. Frequency shifts

Abstract

Measurements have been made on the vibrational absorption bands of HCN, DCN and other compounds containing CH and CN groups, used as solutes in a number of solvents. The results have been used to examine the importance of bulk dielectric effects and of specific solute-solvent interactions in determining the positions of the absorption bands. Some ideas about the method of interaction between the solute and solvent can be obtained from the results in series of solvents of different types, and alternative mechanisms for this interaction are suggested. It is possible to relate the observed changes in the band positions with quantitative measures of the electron density at likely centres of interaction, based upon the Taft inductive and resonance factors of groups or upon quadrupole coupling constant data. Comparisons have been made with other vibrational chromophores such as C = O, and differences can be inferred about the relative significance of bulk dielectric effects and specific interactions in different cases. All the results have been discussed with reference to current theories of solvent effects on the dissolved oscillator molecule.