Part I of this thesis describes two quite different S(,RN)1 processes. The reaction of dialkyl phosphite ions with (alpha)-nitro halides and (alpha)-nitro sulfones occurs by a thermally initiated process. Anions of secondary nitroparaffins couple with alkylmercury halides to form tertiary nitroparaffins, mercury metal, and halide ion by a photo-initiated process;In Part II, a series of photo-initiated radical chain substitution reactions of 1-alkenyl mercurials is described. The series includes (1) the decomposition of 1-alkenylmercury mercaptides to form mercury metal and 1-alkenyl sulfides, (2) the reaction between alkyl or aryl disulfides, aryl diselenides, or aryl ditellurides with 1-alkenylmercury halides to form 1-alkenyl sulfides, selenides, or tellurides and a halomercury mercaptide, selenide, or telluride salt, (3) the reaction of bis1-alkenylmercury compounds with phenyl disulfide to form mercury metal and 1-alkenyl phenyl sulfides, (4) the reaction of organic halides with 1-alkenylmercury halides to form substituted alkenes and a mercuric halide salt, and (5) the coupling of 1-alkenylmercury halides with alkyl or aryl sulfinate, dialkyl phosphite, or butyl phenylphosphonite ions to yield mercury metal, halide ion, and a 1-alkenyl sulfone, dialkyl phosphonate, or butyl phenylphosphinite. The reactions have been shown in most cases to proceed by free radical addition to the 1-position of the alkenylmercury compound followed by loss of a paramagnetic mercury(I) species.