Relationship between the Broad OH Stretching Band of Methanol and Hydrogen-Bonding Patterns in the Liquid Phase

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Abstract
The OH stretching (νOH) band of methanol observed in condensed phase has been analyzed in terms of hydrogen-bonding patterns. Quantum chemical calculations for methanol clusters have revealed that broadening of the νOH envelope is reasonably reproduced by considering nearest and next-nearest neighbor interactions through hydrogen bonding. Because the hydrogen bond formed between donor (D) and acceptor (A) is cooperatively strengthened or weakened by a newly formed hydrogen bond at D or A, we have proposed the following notation for hydrogen-bonding patterns of monohydric alcohols: aDDAdAaA, where a is the number of protons accepted by D (aD) or A (aA), and dA is the number of protons donated by A. The indicator of the hydrogen-bond strength, which is given by MOH = aD + dA − aA, is correlated well with the νOH wavenumber of the methanol molecule D participating in the aDDAdAaA pattern. The correlation between MOH and the hydrogen-bonding energy of the aDDAdAaA pattern has also been deduced from the calculation results for the clusters. The νOH bands of methanol measured in the CCl4 solution and pure liquid have been successfully analyzed by the method proposed here.

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