PHOTO VALENCE ISOMERIZATION OF 8,9-BIS(N-CYCLOHEXYLCARBAMOYLOXYMETHYL)-[6]PARACYCLOPHANE

Irradiation in the wavelength range of lambda = 270 - 320 nm of 8,9-bis(N-cyclohexylcarbamoyloxymethyl)-[6]paracyclophane (1b) in dilute fluid solutions produces the 1,4-Dewar isomer 2b in a quantum yield of 2.8% while the quantum yield of the rearomatization is 19% in heptane at room temperature. A photostationary equilibrium may be attained which depends strongly on the wavelength of irradiation. At lambda = 290 nm 76% of the [6]paracyclophane isomer lb is obtained whereas at lambda = 310 nm 83% of the Dewar isomer 2b is formed in ethanol. The thermal back reaction 2b --> 1b follows the Arrhenius law (E(a) = 95.9 +/- 4.0 kJ/mol, Ig A = 10.6 +/- 0.4 in heptane). By irradiating lb with lambda < 270 nm the prismane isomer 3b is formed via the Dewar isomer 2b.