Rate Constants and Arrhenius Functions for Rearrangements of the 2,3-Dimethyl-3-butenyl and (2,2-Dimethylcyclopropyl)methyl Radicals

Article abstract of DOI:10.1021/jo00272a042

Rate constants for the rearangement of the 2,2-dimethyl-3-butenyl radical (1) to the 1,1-dimethyl-3-butenyl radical (3) via the intermediate (2,2-dimethylcyclopropyl)methyl radical (2) were measured over the temperature range 74 to -78 deg C by the competition method using the reaction of radical 1 with Bu3SnH as the basis reaction.Rate constants for ring opening of radical 2 to both 1 and 3 were measured over the temperature range 50 to -78 deg C by competition against reaction of 2 with PhSH.Arrhenius functions for the 1 to 3, 1 to 2, 2 to 1, and 2 to 3 conversions were calculated; at 25 deg C, the rate constants for these conversions are 4.8*10⁶, 5.6*10⁶, 1.2*10⁸, and 7.7*10⁸ s^-1, respectively.At room temperature, cyclization of gem-dimethyl-substituted radical 1 is accelerated by about 3 orders of magnitude over its parent, 3-butenyl radical.Ring opening of 2 is about 1 order of magnitude faster than ring opening of its parent, cyclopropylcarbinyl radical.For the 1 to 2 conversion, K₁₂ varies from 0.05 at 25 deg C to 0.02 at -78 deg C, ΔH₁₂ is 1.0 kcal/mol, ΔS₁₂ is -2.7 eu, and ΔG₁₂ at 25 deg C is 1.8 kcal/mol.