SOLVENT ISOTOPE EFFECTS AND TRANSITION-STATE SOLVATION IN BASIC METHANOLYSIS OF ESTERS

Aryl methyl carbonates and aryl acetates undergo methoxide-catalyzed methanolysis in CH3OD 1.5-2.1 times faster than in CH3OH. The magnitudes of isotope effects and entropies of activation indicate that the gross isotope effects originate in an increase in structure of the solvent as methoxide ion partially adds to the substrate carbonyl groups, probably accompanied by an increase in solvent librational frequencies. The substituent-induced variations in the isotope effects and entropies of activation are most easily interpreted as involving changes in hydrogen-bonding strength for solvent molecules. © 1969, American Chemical Society. All rights reserved.