LASER FLASH-PHOTOLYSIS STUDY OF ARYLCYCLOPROPYLCARBENIUM IONS - CATION STABILIZING ABILITIES OF CYCLOPROPYL AND PHENYL GROUPS

Arylcyclopropylcarbenium ions, Ar(c-Pr)CH+, were generated as transien t intermediates by laser flash photolysis (LFP) of trans-2,3-diphenyla ziridinimines of aryl cyclopropyl ketones in 2,2,2-trifluoroethanol (T FE). The carbocations are thought to arise by way of diazo compounds a nd carbenes. Rate constants for the unimolecular decay in TFE and for the bimolecular reaction with methanol in TFE were obtained for Ar(c-P r)CH+ and for analogous arylphenylcarbenium ions, ArPhCH(+). Within th ese series, the cation stabilizing abilities of cyclopropyl and phenyl groups are found to be similar in magnitude. However, cyclopropyl res ponds more strongly than phenyl to increasing electron demand. Hence c yclopropyl is superior to phenyl in cation stabilizing ability for Ar = Ph but inferior to phenyl for Ar = 4-MeOC(6)H(4).