Clocking Tertiary Cyclopropylcarbinyl Radical Rearrangements

Three independent methods have been employed to estimate the rate constant, k1, for ring-opening of the 2-cyclopropyl-2-propyl radical, 1, at room temperature. These three estimates are based on chemical trapping of 1 and the ring-opened 4-methylpent-3-ene-1-yl radical by thiophenol (k1 = (1.65 \ub1 0.41) 7 107 M-1 s-1), 9-azabicyclo[3.3.1]nonane-N-oxyl (k1 = (1.76 \ub1 0.34) 7 107 M-1 s-1) and 2,2,6,6-tetramethylpiperidine-N-oxyl (k1 = (2.1 \ub1 0.4) 7 107 M-1 s-1) and absolute rate constants for nonrearranging radicals structurally related to 1. The mean value for k1 ((1.84 \ub1 0.4) 7 107 M-1 s-1) should be used when 1 is employed as a tertiary alkyl free radical clock at ambient temperatures.NRC publication: Ye