C-13 NMR SPECTROSCOPIC STUDY OF THE TAUTOMERIC EQUILIBRIUM IN P-PHENYL SUBSTITUTED BENZOYLACETONES

Solution C-13 NMR chemical shifts are reported for a series of p-phenyl substituted benzoylacetones which undergo a fast, intramolecular proton-transfer reaction between both possible enol tautomers. This information, together with C-13 NMR spectroscopic data for related non-exchanging model compounds, allows the study of substituent-induced equilibrium shifts. The results show a systematic trend: electron-withdrawing para groups shift the equilibrium towards the methyl keto form.