Anharmonicity and Hydrogen Bonding. The in-plane OH Bending and its Combination with the OH Stretching Vibration

Abstract

The infrared spectra of isopropanol, tert-butanol, and their deuterated homologues were measured between 1600 and 1160 cm−1 in a mixture of CCl3F and methylcyclohexane-d14 at temperatures ranging from 20 to −182 °C. The assignments of the in-plane OH deformation (δOH) bands of alcohols are confirmed by these low temperature measurements. An explanation is proposed for the great apparent differences between the δOH frequencies of primary and secondary alcohols on the one hand, and tertiary alcohols on the other. The effect of temperature on the δOH frequency of hydrogen bonded alcohols is found to be slight. Hydrogen bonding increases significantly the anharmonic coupling constant between νOH and δOH It remains, however, much smaller than the anharmonicity constant of νOH itself.