Electron transfer chain reactions leading to substitution in electronegatively substituted benzene derivatives can be observed with alkylmercury halides in the presence of proton accepters such as DABCO. Promotion by base involves the abstraction of a proton from the substituted cyclohexadienyl adduct radical to form a radical anion which readily transfers an electron to RHgX with the regeneration of R-.. Aromatic substitutions involving t-Bu-. are highly regioselective and yield products of only para attack for PhCHO, PhCOCH3, PhCOCMe3, PhCOPh, PhCN, phthalimides, or 1,2-dicyanobenzene. The ortho/para substitution products are observed for isophthaldehyde or 1,3-dicyanobenzene, while 1,4-dicyanobenzene yields the ortho substitution product. At 25-35 degrees C substitution by t-Bu-. ortho to an ester group is not observed and m-or p-cyanobenzoate esters yield only products of substitution ortho to the cyano group. With the isopropyl radical substitution ortho to the ester function is observed with:diethyl isophthalate. Intramolecular radical cyclizations of the radical adducts of 1-aryl-4-penten-1-ones leading to alpha-tetralones. is also promoted by the presence of DABCO. When the aryl group contains a para eater function, spirocyclization occurs leading to a rearrangement acyl radical which,can be oxidized by t-BuHgCl to the acyl cation and the carboxylic acid.