Stereochemistry crossover from retention to inversion of configuration (or vice versa) in individual reaction series involving alkoxide reagents is reported for the leaving groups OPh, SMe, and F. The reactant is R3Si*X (R3Si* is α-naphthylphenylmethylsilyl). Mechanistic implications of this work are discussed and further support for the Sni-Si and Sn2-Si mechanisms is adduced. © 1969, American Chemical Society. All rights reserved.