Vinyl carbanions. 2. Simultaneous hydrogen-deuterium exchange and addition of ethyl [2H]alcohol to trans-cinnamonitrile catalyzed by sodium ethoxide

The kinetics of the simultaneous addition of ethyl (/sup 2/H)alcohol to trans-cinnamonitrile and the H--D exchange at C/sub ..cap alpha../ catalyzed by sodium ethoxide have been studied. The observed rate equation for the addition is R = A(trans-cinnamonitrile) + B, where A and B are constants which depend on the initial concentrations of olefin and base. The forward (k/sub 1/) and the backward (k/sub -1/) rate constants of the nucleophilic addition step are (3.72 +- 0.51) x 10/sup -4/ l. mole/sup -1/s/sup -1/ and (9.58 +- 1.20) x 10/sup 4/ s/sup -1/, respectively. The equilibrium constant for the overall addition reaction is K = (3.9 +- 0.2) x 10/sup -2/ l. mole/sup -1/. The H--D exchange is faster than the addition reaction and takes place via the vinyl carbanion derived from the olefin. Cis to trans isomerization occurs during the addition of ethyl (/sup 2/H)alcohol to cis-cinnamonitrile. Based on kinetic data, it is suggested that this isomerization takes place by an addition--elimination mechanism.