An ab initio approach to creating a simple stable enol

Abstract

Ab initio molecular orbital theory is used to examine the effect of four substituents (CN, NO₂, NO and CHO) which are π-electron acceptors and σ-electron acceptors on the keto-enol equilibrium in the acetaldehyde/vinyl alcohol system. Each substituent destabilizes the keto isomer and stabilizes the enol isomer as desired and hence decreases the enol-keto energy difference. For the NO and CHO substituents, the effect is sufficiently large that the enol isomer is predicted to be slightly lower in energy than the keto form. The conformational preferences of the keto isomers are discussed in detail and a conformational potential energy map is presented for malondialdehyde.