bond in three series of alkenylsilanes, R3Si·[CH2]n·CHCH2(R = Me, Ph, or Cl) toward addition by the trichloromethylradical have been determined, and the relative reactivities of vinyl- and allyltrimethylsilane toward free radicaladdition by n-dodecanethiol have been investigated. The factors influencing the reactivities of the various alkenylsilanes toward radicaladdition reagents are discussed.