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Proton tautomerism is a general phenomenon in organic molecules and plays a vital role in many fields of chemistry and biochemistry. The tautomerism of salicylideneanilines eq(1) has attracted a considerable attention because it is closely related to thermo-and photochromism. Salicylideneanilines greatly favor the enol form over the cis-keto form in the gas phase. We demonstrate here that the instability of the cis-keto form is substantially reduced by intermolecular hydrogen bonding and also by self-association, on the basis of our variable temperature X-ray crystallographic and UV-vis absorption spectroscopic studies.
Civalleri et al. (Tue,) studied this question.