Abstract
The enol content and equilibrium free energies for the keto-enol tautomerism have been determined for a series of 1,3-diketones, at 40°C, in deuterochloroform and dimethylsulfoxide-d 6 (DMSO), by 1H n.m.r.. Compounds containing methyl, phenyl, t-butyl, 2-thienyl, trifluoromethyl and ethoxy groups have been examined. The equilibrium free energies in DMSO are characterized by a linear additivity effect, and substituent parameters, representing the variation produced by the substituent, have been calculated. Equilibrium enthalpy and entropy have been obtained in the range of temperature 20–60°C. A correlation between enolic 1J CH= coupling constants and equilibrium free energies in DMSO is discussed in terms of substituent effects on the energy of the enol.
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