10.1021/jo061868w.s001 John H. Horner John H. Horner Martin Newcomb Martin Newcomb Kinetic Studies of a Fast, Reversible Alkene Radical Cation Cyclization Reaction American Chemical Society 2007 rate constants acyclic product 10 Reversible Alkene Radical Cation Cyclization ReactionThe fluoroalcohols RfCH 2OH cation 2007-03-02 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Kinetic_Studies_of_a_Fast_Reversible_Alkene_Radical_Cation_Cyclization_Reaction/3020713 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 formed acyclic radical cation is a resonance hybrid with partial positive charge in both double bonds of 1,1-diphenyl-7-methyl-1,6-octadiene (<b>10</b>). Thiophenol trapping was used as the competing reaction for kinetic determinations. The acyclic radical cation rapidly equilibrates with a cyclic distonic radical cation, and thiophenol trapping gives acyclic product <b>10</b> and cyclic products, mainly <i>trans</i>-1-(diphenylmethyl)-2-(1-methylethenyl)cyclopentane (<b>11</b>). The rate constants for cyclization at ambient temperature were <i>k</i> = (0.5−2) × 10<sup>10</sup> s<sup>-1</sup>, and those for ring opening were <i>k</i> = (1.5−9) × 10<sup>10</sup> s<sup>-1</sup>. Laser flash photolysis studies in several solvents show relatively slow processes (<i>k</i> = (2.5−260) × 10<sup>5</sup> s<sup>-1</sup>) that involve rate-limiting trapping reactions for the equilibrating radical cations. In mixtures of fluoroalcohols R<sub>f</sub>CH<sub>2</sub>OH in trifluoromethylbenzene, variable-temperature studies display small, and in one case a negative, activation energies, requiring equilibration reactions prior to the rate-limiting processes. Fast equilibration of acyclic and cyclic radical cations implies that product ratios can be controlled by the populations of the acyclic and cyclic species and relative rate constants for trapping each.