Acid-catalyzed ketone-enol tautomerism →+OH OH H H u H Base-catalyzed ketone-enol tautomerism 0 BH 一BH OH B H HB H O O - O - －BH H + OH BH －B Acid-catalyzed ketone-enol tautomerism H O H + H OH H OH + + －H + OH H + －H + Base-catalyzed ketone-enol tautomerism