Raman effect and hydrogen bonds - Part VI. Chelate compounds: Esters of salicylic acid and their mixtures
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The Raman spectra of methyl, ethyl,n-butyl, iso-amyl and phenyl esters of salicylic acid have been studied. Besides the bright frequency attributable to the C=O group of the chelate structure, a weaker line corresponding to the unchelate molecule has been observed in each case. Thus the liquids contain the two types existing in equilibrium, the chelate molecules being predominant. The extent of the lowering of the C=O frequency brought about by chelation indicates that this type of intamolecular hydrogen bond is strong. This is also supported by the study of the mixtures of methyl and ethyl salicylates, with chloroform, phenol, dioxan and acetic acid. The spectra are unaffected showing that the chelate bond cannot be broken by anionoid and cationoid solvents and that salicylates cannot function as other esters and phenols do in breaking down hydrogen bonds.
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