Competition between substitution and elimination in the reactions of dianions with substituted and cyclic alkyl halides.

摘要

In the first study, we have examined alkyl chlorides with strong electron-withdrawing groups at the beta-carbon and a new set of dianions. The results indicate strong activation of the elimination pathway when the beta substituent is cyano or carboxyl and collision-controlled rates are observed. In all cases, these substituents induce a high percentage of elimination (E2) and the reactivity of the alkyl chlorides, based on the substituents, is cyano approx propionate phenyl approx chloro > methoxy. The results are consistent with predictions based on ab initio calculations. In the second study, the rates are typical for secondary bromides and remarkably consistent for the rings larger than cyclobutane. However, the results are strongly tilted towards elimination suggesting that it is difficult to accommodate Walden inversions in these rings. With the weaker nucleophile, more substitution is observed, but the rates are considerably lower. Computational studies on these systems are underway.