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

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Abstract
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 [Formula: see text] hydrogen bonds) and intermolecular ([Formula: see text] 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 [Formula: see text] hydrogen bond results in significantly slower rotational relaxation of the alcohol molecule. The enthalpy differences between the two conformers are found to be 1.52 ± 0.13, 1.57 ± 0.15, 1.53 ± 0.08, 1.06 ± 0.13, and 1.15 ± 0.11 kcal/mol for the compounds in the order stated above.

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