Leslie Fradkin - University of Ottawa

Placement: Dalhousie University
Supervisor: Dr. Fran Cozens

b-Heterolysis of Phenoxy-substituted Radicals

The reactions of b-substituted carbon-centered radicals with various substituents in the b-position were studied using nanosecond laser flash photolysis. Four 1-acetoxy-2-phenoxy-1-(4-methoxyphenol) compounds were synthesized and analyzed with four different substituents in the para position of the phenoxy group: CN, CH₃, H, and CF₃. In addition, three 1,3-ditoluyl-2-propanone compounds that were disubstituted with various leaving groups, OH, OSO₂Me, and OPO(OEt)₂ were also synthesized. Both of these groups of compounds are known to form carbon-centered radicals when irradiated by nanosecond laser flash photolysis. These b-substituted radicals were then expected to undergo b-heterolysis to form a radical cation which is detectable using UV spectroscopy. The compounds were irradiated in non-ionizing solvents such as acetonitrile (AcN) as well as more ionizing solvents such as 2,2,2-trifluoroethanol (TFE). The irradiation was also performed with the samples incorporated into Faujasite zeolite NaY. It was determined that b-heterolysis does not occur for p-substituted phenoxyl radicals even in highly ionizing solutions or in zeolites. The disubstituted 1,3-ditoluyl-2-propanone compounds readily decarbonylated to form the carbon-centered radical. The subsequent b-heterolysis then occurred in the case of the methyl sulfonate leaving group only. The phosphate or hydroxyl leaving group did not appear to come off neither in solution nor in zeolite. The rate constant for the heterolysis increased with the ionizing character of the solvent used. The rate of decay of the radical cation also increased significantly with the nucleophilic character of the solvent.