DIRECT CATALYTIC EFFECT AND FINE MODULATION OF SOLVENT IN THE KETO-ENOL ISOMERIZATION OF AMIDES

The modulation of proton transfer reactions by environmental effects has been investigated for the case of keto-enol isomerization of formamide. Formation of long-lived adducts with a single water molecule or of formamide dimers enhances the reaction rate and shifts the equilibrium towards the lactam form. The effect of bulk solvent on these adducts is small, whereas it further stabilizes the keto form of free formamide. Zero point and entropy effects on the thermodynamics and kinetics of the reaction are generally negligible and do not modify the above general trends. Significant reaction rates are obtained well under the energy barrier due to tunneling. They are, however, smeared out when going from microcanonical to canonical ensembles.