The relative magnitude of the hyperconjugative stabilization of vinyl cations by adjacent CM bonds (M= Si, Ge, Sn; the@-effect) has been examined by measuring the rate constants for the protonation and subsequent protiodemetalation of group 14 metalated (trimethylsily1)- acetylenes (RsMC= CSiMes). The relative@-effect arising from the second-order rate constants Sn>> Ge> Si (maximum kdksi= 1@, 5 X lo2, 1, respectively) follows the same ...