Structural Information from the Integrated Intensity of the OH-Stretching Band of Saturated Alcohols

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Abstract
The integrated intensity, A, of the free OH-stretching band of a large number of noncyclic and six-membered cyclic saturated monohydroxy compounds has been studied as a possible source of structural information. The intensity of primary alcohols proves to be constant, viz., 16.8 ± 0.5 km/M. No factors have been found that influence this value. The standard A-value for secondary alcohols is 13.8 ± 0.4 km/M. OH-rotamers without trans-H-Oxygen-lone-pair interaction show a lower intensity; factors influencing the rotamer distribution might thus affect the overall A-value. A significant decrease is observed when a γ-methyl group is situated (very) close to and therefore strongly interacts with a lone pair of the oxygen atom. The standard A-value for tertiary alcohols is 11.2 ± 0.6 km/M. Initially all rotamers have the same A-value, but for the secondary ones a strongly interacting γ-methyl group may cause an appreciable intensity lowering. Besides, strong sterical interactions between the three alkyl substituents at the α-C-atom usually give rise to small changes in the intensity. The overall conclusion is that the integrated intensity proves to be a useful source of structural information.

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