The effects on the rates of cleavage of 3-ClC₆H₄CH₂MMe₃ and 3,5-Cl₂C₆H₃CH₂MMe₃ compounds with M = Si and Sn have been examined for (a) various concentrations of NaOMe-MeOH; (b) various concentrations of H₂O in NaOHH₂O-eOH; and (c) variation of R from Me to Et, i-Pr and t-Bu for metal alkoxide-ROH mixtures. Rates have also been measured for cleavages in NaOCH₂CF₃HOCH₂CF₃-Me₂SO. In all cases there are differences in behaviour between the silicon and tin compounds which are consistent with the postulated difference in the mechanisms of their reactions.