Carbonyl Addition Reactions: Factors Affecting the Hydrate–Hemiacetal and Hemiacetal–Acetal Equilibrium Constants

Equilibrium constants for hydrate–hemiacetal interconversion in aqueous solution at 25° have been measured for four fluorinated carbonyl compounds: compound, alcohol, K 4 (M −1 ): CF 3 CHO, C 2 H 5 OH, 2.3; CF 3 COCH 3 , CH 3 OH, 1.0; CF 3 COPh, CH 3 OH, 3.5; CF 3 COCF 3 , CH 3 OH, 0.14. These values, combined with values from the literature, permit an examination of substituent effects upon the equilibrium constant forFormula: see textThe free energy change for this process, corrected for symmetry and steric effects, follows the equationFormula: see textThus electronic effects upon this equilibrium are generally small and in fact are often smaller than steric effects.This analysis permits and justifies the calculation of free energies of formation of Formula: see text compounds from the (more generally measurable) free energies of formation of the analogous Formula: see text compounds.