PHOTOLYSIS OF AZOALKANES - REACTIONS AND KINETICS OF THE 1-CYCLOPROPYLCYCLOPENTANE-1,3-DIYL BIRADICAL AND THE 1-CYCLOPROPYLCYCLOPENTYL RADICAL

The cyclopropylcarbinyl (CPC) rearrangement rates of 1-cyclopropylcyclopentyl (10a) and 1-cyclopropylcyclohexyl (10b) radicals to yield 34a,b are found to be 1.45 x 10(7) and 1.1 x 10(7) s-1 at 24.7-degrees-C, respectively. These values, which are based on thiophenol trapping of 10a,b are 6-9 times slower than that of the parent cyclopropylmethyl radical. Ring closure of homoallylic radical 34a proceeded at a rate of 5.5 x 10(4) s-1, which is 7 times faster than that of 3-butenyl. No 1,5-hydrogen shift was found in 34a. The triplet 1,3-biradical 6T analogous to 10a was produced by triplet-sensitized photolysis of 1-cyclopropyl-2,3-diazabicyclo[2.2.1]hept-2-ene (11). Biradical 6T rearranges to 9E and 9Z, the latter of which undergoes rapid intramolecular disproportionation to 46Z. On account of its geometry, the E isomer cannot lead directly to a stable product; hence, it recloses to 6T (k(ra) = 1.2 x 10(5) s-1) but, interestingly, not to 6S. If the CPC rearrangement rate of 6T is taken to equal that of 10a, we calculate from the product distribution that the lifetime of 6T is 59 ns. This figure is only half the lifetime of the parent cyclopentane-1,3-diyl (1), showing that the perturbing effect of cyclopropyl is similar to that of methyl.