Stable quinonoid nitronates. A structure investigation of ethyl 2-nitrophenyl-pyruvate anions based on nuclear magnetic resonance spectroscopy and MO-SCF-HAM/3 calculations

Abstract

Ethyl 2-nitrophenylpyruvate anions have o-quinonoid nitronate structures while their corresponding acids are aromatic α-enol and/or α-keto esters. A semiempirical quantum chemical study of the different tautomers of these systems using HAM/3 has suggested a non-planar ring conformation of the nitronic acids and the nitronates. The presence of a hydrogen bond between 6–H and its neighbouring carbonyl oxygen in the title compound is inferred by an unusually low field proton resonance.