PART I. PHOTOCHEMISTRY OF 1-AZOADAMANTANE: REACTIONS OF 1-ADAMANTYL RADICALS IN VARIOUS SOLVENTS. PART II. THE QUEST FOR THE CARBON-CENTERED BETA-AZO RADICAL VIA HOMOLYSIS OF ACYCLIC AND CYCLIC AZO COMPOUNDS

Part I. The tritium isotope effect for hydrogen atom abstraction by the 1-adamantyl radical in cyclohexane was determined to be 103, confirming the exceptionally large deuterium isotope effect found earlier for this process. While the Noyes model accounts for the cage effect in the thermolysis of cis -1-azoadamantane, the non-linear correlation between the yield of cage dimer and solvent fluidity at high viscosities suggests that microviscosity influences the breakdown of the solvent cage. In acetonitrile, 1-adamantyl radicals were found to abstract hydrogen atoms or to add to the nitrile function. The products of cross-recombination between the resulting radicals were identified and quantified. Part II. The carbon-centered $\beta$-azo radical was calculated to fragment under formation of nitrogen with an exothermicity of $\sim$10 kcal/mole. The generation of such a $\beta$-azo radical was attempted by homolytic fragmentation of five acyclic and cyclic $\beta$-substituted azo compounds. Although concerted decomposition of these compounds could cause a drastic rate enhancement, our azo compounds exhibited only a slight rate enhancement (1.5-9 fold) in comparison to the unsubstituted azo compounds. The radical stability of the $\beta$-substituent exerted no influence on the rate of azo fragmentation. The high temperature required for pyrolyses (180$\sp\circ$C) led to complicated product mixtures due to competing bond scission between the azo moiety and the $\beta$-substituent, as well as the decomposition of primary thermolysis products. For $\beta$-azo phosphinites and $\beta$-azo carbonates, the fragmentation was governed by both ionic and radical processes. The tin hydride reduction of a cyclic $\beta$-azo xanthate at room temperature proceeded via intramolecular radical attack on the azo linkage to yield an unusual cyclic thiourea rather than by loss of N$\sb 2$