V. J. Shiner, Joseph W. Wilson, G. Heinemann
Jun 1, 1962
Citations
0
Influential Citations
3
Citations
Journal
Journal of the American Chemical Society
Abstract
The isotopic variant of 3-bromo-3-methyl-1-butyne (I) having all six hydrogens of the two methyl groups replaced by deuterium, undergoes the SN1, carbonium ion solvolysis reaction in 80%'' ethanol at 25 deg 1.84 times slower than I itself. The second-order hydroxide ion-promoted solvolysis, which is an SN1 reaction of the conjugate base, is slowed, by this deuterium substitution, by only a factor of 1.31. This is apparently most reasonable explained in terms of differing demand for hyperconjugation in the two closely related transition states. Replacement of the acetylenic hydrogen by deuterium has very little if any influence on the solvolysis rate of the analogous chloro compound. This represents a vinylog'' of alpha -deuterium substitution and the absence of any isotope effect is consistent with the accepted steric origin of the alpha - deuterium isotope effect. (auth)