Theoretical studies on nitro substitution in keto-enol and imine-enamine tautomeric processes

Abstract

<i>Ab initio</i> studies on the keto-enol tautomerism in nitroacetaldehyde and imine-enamine tautomerism in nitroacetaldimine are carried out by performing optimizations at HF/6-31G* and MP2/6-31G* levels. Final energies are obtained by performing MP4(SDTQ) single point energies on the MP2/6-31G* geometries. The stabilities of the resultant nitrovinylalcohol and nitrovinyalamine have been estimated by studying the 1,5 hydrogen shift in these molecules. The 1,3-hydrogen shifts in nitroacetaldehyde and nitroacetaldimine to give <i>acinitro</i> tautomers are also analysed. The enol and enamine tautomers are stabilized due to intramolecular hydrogen bond upon

nitro substitution. The tautomer energy differences are reduced in keto-enol tautomerism by about 8.7 kcal/mol because of nitro substitution. The generally unstable enamine became more stable than imine by 2.5 kcal/mol on nitro substitution.