Creation of a Simple Stable Enol. The Stabilizing Properties of the Diazonium Substituent

Abstract

Ab initio molecular orbital theory is used to examine the effect of the diazonium substituent (N₂⁺) on the keto-enol equilibrium in the acetaldehyde/vinyl alcohol system. The conformational preferences of the two isomers are examined, and optimized geometries obtained for the best conformers. The diazonium substituent is a strong π-electron acceptor and σ-electron acceptor, and accordingly destabilizes the keto isomer and stabilizes the enol isomer. The effect of the diazonium substituent is sufficiently large to make the enol isomer substantially lower in energy than the keto isomer.