Steric and Electrochemical Effects on Rates of Electron Transfer and SN2 Reactions of 9-(Dialkylamino)fluorenide Ions with Alkyl Halides

Article abstract of DOI:10.1021/ja00185a040

Rate ratios for reactions of PhCH2Cl vs Ph2CHCl with seven 9-(dialkylamino)fluorenide (9-R2NFl(1-)) ions were measured in Me2SO solution.Although the reaction sites in these ions are known to be highly congested and Ph2CHCl is more sterically hindered than is PhCH2Cl, the k^PhCH2Cl/k^Ph2CHCl rate ratios for reactions with 9-R2NFl(1-) ions in Me2SO were all much lower (0.20-4.9) than for the less hindered 9-MeFl(1-) or p-MeOC6H4O- ions (81 and 138, respectively).This suggested that the Ph2CHCl reactions with 9-R2NFl(1-) ions were occuring by single electron transfer(SET) mechanisms, despite the formation of high yields of S_N2-type products.This conclusion was supported by the observation of a close correspondence between SET rates (log k_SET), calculated by using the Marcus equation, and log k_obsd for reactions of 2-R2NFl(1-) ions with both a known single electron acceptor, F3CCH2I, and with Ph2CHCl and (p-ClC6H4)2CHCl.Similar log k_SET vs log k_obsd comparisons for reactions of the 9-R2NFl(1-) ions with PhCH2Cl, c-C6H11Br, and n-BuBr revealed greater disparity.