Dynamic nuclear magnetic resonance study of vinyl formate

EandZConformations of Esters, Thiol Esters, and Amides

“…We have used dynamic NMR spectroscopy to study the possibility that esters, thiol acids, and thiol esters, with groups such as vinyl, phenyl, or hydrogen, which could not provide a pair of electrons to complete an “aromatic” sextet in the Z conformations, would have enhanced populations of the E isomers. The conformational equilibria for S -phenyl thioformate, phenyl formate, vinyl formate, thioacetic acid, and dithioacetic acid could be rationalized in terms of an effect of this type. The ethynyl group also could not support an aromatic sextet in the Z conformation, and an E − Z energy difference of only 1.7 kcal/mol was estimated for ethynyl formate by ab initio calculations.…”