New thermochemical parameter for describing solvent effects on IR stretching vibration frequencies: Communication 1. Assessment of van der Waals interactions

Solvent effects on OH stretching vibrations in several complexes with hydrogen bonding have been investigated by FTIR spectroscopy. To assess the influence of van der Waals (vdW) interactions on frequency shifts, a new parameter of solvent, δcavhS, is proposed. This parameter has been derived from equations describing enthalpy of non-specific solvation. Linear correlation was established between the OH frequency shift (with respect to the gas phase) and parameter δcavhS for a series of complexes of aliphatic alcohols with standard proton acceptors. Linear correlations with δcavhS were also observed for a series of “free” OH and also CO, PO, SO and CBr stretching vibrations. A new method is proposed for estimating the gas-phase stretching frequency from IR spectra of solutions. In addition, frequencies of “free” XH groups in neat bases were deduced from the experimental data.