Vinyl carbanions. Part I. Kinetics of hydrogen–deuterium exchange in fluoren-9-ylideneacetonitrile catalysed by sodium ethoxide

Abstract

The kinetics of hydrogen–deuterium exchange in fluoren 9-ylideneacetonitrile in ethyl [²H]alcohol, catalysed by sodium ethoxide, have been studied. The observed rate equation is (i) where k_ex= 1.15 ± 0.05 l mol^–1 min^–1 at R =k_ex[Olefin][EtO–Na+](i) 30°. N.m.r. did not show any formation of the addition product of ethyl alcohol to this olefin. Hydrogendeuterium exchange of the cis- and trans-isomers of 3-(2-bromophenyl)-3-phenylacrylonitrile, under comparable conditions, occurs without any isomerization. It is suggested, therefore, that exchange takes place via the derived vinyl carbanion and not by an addition–elimination mechanism.