| Abstract
| - The radical cation formed by mesylate heterolysis from the 1,1-dimethyl-7,7-diphenyl-2-mesyloxy-6-heptenyl radical was studied in several solvents. Computational results suggest that the initially formedacyclic radical cation is a resonance hybrid with partial positive charge in both double bonds of 1,1-diphenyl-7-methyl-1,6-octadiene (10). Thiophenol trapping was used as the competing reaction for kineticdeterminations. The acyclic radical cation rapidly equilibrates with a cyclic distonic radical cation, andthiophenol trapping gives acyclic product 10 and cyclic products, mainly trans-1-(diphenylmethyl)-2-(1-methylethenyl)cyclopentane (11). The rate constants for cyclization at ambient temperature were k =(0.5−2) × 1010 s-1, and those for ring opening were k = (1.5−9) × 1010 s-1. Laser flash photolysisstudies in several solvents show relatively slow processes (k = (2.5−260) × 105 s-1) that involve rate-limiting trapping reactions for the equilibrating radical cations. In mixtures of fluoroalcohols RfCH2OHin trifluoromethylbenzene, variable-temperature studies display small, and in one case a negative, activationenergies, requiring equilibration reactions prior to the rate-limiting processes. Fast equilibration of acyclicand cyclic radical cations implies that product ratios can be controlled by the populations of the acyclicand cyclic species and relative rate constants for trapping each.
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