Solvent effects on vibrational spectrum of hydrogen-bonded complex PhOH⋯H 2O. An ab initio study

Abstract

The vibrational features characterising the hydrogen-bonded interaction between PhOH and H 2O have been studied. The vibrational spectra for free and complexed PhOH and H 2O have been predicted by ab initio calculations at different levels: 3–21G/SCF, 6–31G/SCF and 6-31G/MP2. The changes in the vibrational characteristics (vibrational frequencies, infrared intensities and Raman activities) upon hydrogen bonding have been estimated. It was established that the most sensitive to the complexation is the stretching O–H vibration of the phenol site. In agreement with the experiment, its vibrational frequency is shifted to lower wavenumbers. The magnitude of the wavenumber shift is indicative of a relatively strong OH⋯H hydrogen-bonded interaction. The ab initio calculations at different levels predict an increase of the IR intensity up to 50 times and of the Raman activity up to four times. The remaining vibrations (stretching, bending and torsion) are less sensitive to the hydrogen bonding. Their vibrational characteristics are changed to a less extent.