Consecutive Biradicals during the Photolysis of 2,12-Dihydroxy-2,12-dimethylcyclododecanone: Low- and High-Field Chemically Induced Dynamic Nuclear Polarizations (CIDNP) Study

Low- and high-field 1 H chemically induced dynamic nuclear polarizations (CIDNP) have been applied to investigate geminate reactions of consecutive biradicals generated during the photolysis of 2,12-dihydroxy-2,12-dimethylcyclododecanone. The detailed mechanism of the reaction is established. It is shown that the fast chemical transformation (decarbonylation) of the primary acyl-ketyl biradical manifests itself in CIDNP effects in low and high magnetic fields: the difference in the CIDNP field dependencies for the products of the primary and secondary biradicals is observed, and the net and multiplet effects for the products of the secondary bis-ketyl biradical develop in different time scales. The first observation of the CIDNP “memory effect” in biradical reactions is reported. Model calculations of the CIDNP kinetics based on the numerical solution of the stochastic Liouville equation for the Fourier transform of the biradical spin density matrix have been performed, and a good agreement between the theoretical calculations and experimental data has been found.