COMPETITIVE ELECTRON-TRANSFER AND S(N)2 REACTIONS OF AROMATIC RADICAL-ANIONS WITH ALKYL-HALIDES AND METHANESULFONATES

The competition between electron transfer and S(N)2 processes in the r eaction between a number of radical anions of aromatic compounds such as anthracene, pyrene, (E)-stilbene, m-tolunitrile and p-tolunitrile a nd different substrates such as the methyl, ethyl, butyl, 2-butyl, neo pentyl and I-adamantyl halides as well as methyl, ethyl, butyl and 2-b utyl methanesulfonates has been investigated in N,N-dimethylformamide. By using the reaction of the radical anions with the appropriate alky ldimethylsulfonium iodide or trialkylsulfonium iodide as model for an electron transfer process the reaction mechanism could be characterize d by electrochemical means in many of the cases listed. The presence o f an S(N)2 component is found to be related not only to the steric req uirements at the substrate but also to the magnitude of the driving fo rce for the electron transfer process. Ln general, the higher the stan dard potential of the aromatic compound is or the poorer the substrate is as electron acceptor, the more important the S(N)2 mechanism becom es. An analysis of the substitution products obtained in the reaction between anthracene radical anion and the different substrates shows a considerable rise in the yield of the 9-alkyl-9,10-dihydroanthracene i somer as the magnitude of the S(N)2 component increases.