The ratio, (Kc/Kr)cage, of the rate of coupling of the 1-phenylethyl radical with the benzyl radical to the rate of its rotation with respect to the benzyl radical in the solvent cage has been determined for several solvents. The optically pure title compound, (−)-(S)-4, has been prepared and its absolute configuration determined. Thermal decomposition of (−)-(S)-4 yields (−)-(R)-1,2-diphenylpropane, (−)-(R)-9, with partial retention of configuration. The maximum rotation of (−)-(R)-9 has been determined. At 100° in benzene, cyclohexane, chlorobenzene, (all containing ca. 1 M butanethiol) and butanethiol, the cage effects for the decomposition of (±)-4 were found to be 28.3, 31.7, 33.4, and 18.2%, respectively. Under these conditions (−)-(R)-9 was formed from (−)-(S)-4 with 10.3, 10.9, 13.0, and 17.3% net retention of configuration, respectively. A simple expression for (Kc/Kr)cage can be derived:[Formula: see text]F is the fraction of radicals consumed within the solvent cage and f is the fraction of radicals consumed within the solvent cage that disproportionate. Under the above conditions values for (Kc/Kr)cage were found to be 0.059, 0.069, 0.090, and 0.070, respectively. The values of the cage effect and (Kc/Kr)cage given were calculated assuming f = 0.1, but change little if f is assumed to be 0. The relevance of these results to the stereochemistry of the Wittig and Meisenheimer rearrangements and of the decomposition of diacyl peroxides is discussed.
Optically Active Triptycenes. VII. Synthesis, Optical Resolution and Absolute Configuration of 3-Chloro and 4-Chloro-7-substituted Triptycenes.
