Nature of the Hydrogen Bond. II. The Effect of Hydrogen Bonding and Other Solute-Solvent Interactions upon the Shape and Intensity of the Infrared OH Band of Phenol

Abstract

The hydrogen-bonded OH bands of phenol are studied in ternary systems, each of which is composed of phenol, a proton acceptor, and a solvent. The acceptors used are ethyl ether, ethyl acetate, acetonitrile, and hexamethylene tetramine. It is confirmed that the frequency, shape, and molecular extinction coefficient of the band are not changed by the concentration of the acceptor, as far as the latter is smaller than ca 2 mole/liter. The spectra are slightly modified by further increase of the concentration of the acceptor. These modifications are in all cases far smaller than the modification due to the hydrogen bonding, and the peak intensities remain nearly constant. The equilibrium constants for the formation of the hydrogen bond are determined for all acceptors and the heat of formation is determined for the case of hexamethylene tetramine. It is found that the decrease of frequencies of the hydrogen-bonded OH bands is not strictly parallel to the increase of equilibrium constants.