The competitive rate data and Taft relationships for the coupling of bromomagnesium n-butyl (substituted phenyl) cuprates with alkyl bromides show that selective n-butyl transfer can be explained by an oxidative addition mechanism. Taft reaction constants also show that the residual group FG-C 6 H 4 in the mixed cuprate n-Bu(FG-C 6 H 4 )CuMgBr changes the ability of the copper nucleophile to react with the electrophile RBr. These results provide support for the commonly accepted hypothesis regarding the dependence of the R 1 group transfer ability on the strength of R 2 -Cu bond in reactions of R 1 R 2 CuMgBr reagents.

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