Reaction Mechanism in Crystalline Solids: Kinetics and Conformational Dynamics of the Norrish Type II Biradicals from α-Adamantyl-<i>p</i>-Methoxyacetophenone

In an effort to determine the details of the solid-state reaction mechanism and diastereoselectivity in the Norrish type II and Yang cyclization of crystalline α-adamantyl-<i>p</i>-methoxyacetophenone, we determined its solid-state quantum yields and transient kinetics using nanocrystalline suspensions. The transient spectroscopy measurements were complemented with solid-state NMR spectroscopy spin–lattice relaxation experiments using isotopically labeled samples and with the analysis of variable-temperature anisotropic displacement parameters from single-crystal X-ray diffraction to determine the rate of interconversion of biradical conformers by rotation of the globular adamantyl group. Our experimental findings include a solid-state quantum yield for reaction that is 3 times greater than that in solution, a Norrish type II hydrogen-transfer reaction that is about 8 times faster in crystals than in solution, and a biradical decay that occurs on the same time scale as conformational exchange, which helps to explain the diastereoselectivity observed in the solid state

Supported Gold Nanoparticles as Efficient Catalysts in the Solventless Plasmon Mediated Oxidation of <i>sec</i>-Phenethyl and Benzyl Alcohol

Surface plasmon excitation of supported gold nanoparticles in the presence of H₂O₂ leads to selective oxidation of <i>sec</i>-phenethyl and benzyl alcohols to the carbonyl products acetophenone and benzaldehyde, respectively, in the absence of additional solvents. Light-emitting diodes are compared with microwave irradiation as excitation sources. Hydrotalcite, ZnO, and Al₂O₃ have been chosen as the solid supports. The overall efficiency of the alcohol oxidation was found to be largely dependent on the nature of the support, with hydrotalcite-derived nanocomposites giving the highest conversions to product, yielding 90% acetophenone after 40 min of LED irradiation. The mechanism for plasmon-mediated alcohol oxidation is believed to involve a significant contribution from the support itself, with adsorption of the alcohol substrate and progression of the oxidation reaction being largely facilitated by the basicity of the support used