The Free OH Stretching Vibration

However, this overall range 3700—3500 cm is considerably greater than is found experimentally using unassociated alcohols or phenols in non-polar solvents. The frequency range for each class is very narrow, and the overall spread is no greater than 3650-3590 cm This is the range quoted in Table 6. Fox and 

Martin [10], for example, find the free OH absorptions of a considerable series of aliphatic and aromatic alcohols between 3636 cm and 3618 cm Kuhn [74] has also carried out accurate measurements of the free OH frequencies on a range of thirty-five alcohols and phenols. In all cases the absorption occurred between 3644 and 3605 cm . Within a class of compounds the overall range is smaller still and the free OH band of a large number of 1 2-diols [97, 132] occurs at 3630 5 cm . Similarly, phenols are grouped together with aj3-unsaturated alcohols and absorb at the bottom of the overall range [74, 98]. The influence of the aromatic 

These values all relate to free OH absorptions in non-polar solvents, and small changes occur with alterations in the polarity of the solvent and with changes of temperature and pressure. The changes with solvent have been shown to arise mainly from association effects so that the magnitude of the shift will depend directly on the basic character of the solvent acceptor site, and on the acidity of the alcohol. Phenol in ether shows a very large shift whereas methanol in a solvent of low polarity will show only a small one. Changes with temperature [100, 162] and with pressure [101] are small, and arise from alterations in the distances separating the individual molecules. 

The free OH stretching frequencies of N—OH groups in oximes are similar to alcohols and appear [136—138] between 3650 and 3500 cm .  

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Grubbs WT, Dougherty TP, Heilweil EJ. Bimolecular interactions in (Et)3SiOH base CCl4 hydrogen-bonded solutions studied by deactivation of the free OH-stretch vibration. J Am Chem Soc 1995 117 11989-11992. 

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