Infrared Absorption Band Shape Studies: Fundamental OH Stretching Vibration of Benzyl Alcohol Conformers in Dilute Carbon Tetrachloride Solution

The fundamental OH stretching doublet in the i.r. spectra of a series of a monomeric p-X-benzyl alcohols (X = OCH3, CH3, H, Cl, NO2) observed in dilute CCl4 solution over the temperature range −5 to+40 °C is resolved into two components corresponding to different molecular conformers, using digital computing techniques and a Cauchy–Gauss sum band model. The temperature and substituent dependence of frequencies, band shape indices, and band widths are discussed in terms of intramolecular (electronic displacements and hydrogen bonds) and intermolecular ( and π–σ electron donor–acceptor) interactions. The OH band shapes, which range from 60–98% Cauchy character, reflect variations in the intermolecular interactions which impede molecular re-orientation, and can be correlated with the electronic nature of X and the molecular conformation. The formation of an intramolecular hydrogen bond results in significantly slower rotational relaxation of the alcohol molecule. The enthalpy differences between the two conf...