Experimental and computational studies for various organic systems

The electronic properties and the thermodynamic preferences for O 2 addition to various tetrathiatriarylmethyl (TAM)-type triarylmethyl (trityl) radicals were experimentally and theoretically investigated. The radicals' stability in the presence of O2 and biological milieu was also experimentally assessed. Results showed that H substitution on the aromatic ring affects the trityl radical's stability and may lead to substitution reactions in cellular systems. We proposed that this degradation process involves an arylperoxyl radical that can further decompose to alcohol or quinone products. Computational approaches were also being used to search for spin probes with improved stability and enhanced chemical and biological properties.; A signature absorbance at 392 nm, which is generated from acetonitrile solutions of N-hydroxypyridin-2-thione in the presence of trans-stilbene, was used in competitive laser flash photolysis (LFP) experiments to determine rate constants of reactions for hydroxyl radical with sixteen different benzene derivatives. Structure-reactivity relationships for the reactions of hydroxyl radical with these benzene derivatives were derived. Computational studies were employed to reveal the details of these reactions. The tautomerism and photochemistry of N-hydroxypyridones (NHPs) and N-hydroxypyridinethiones (NHPTs) were also studied theoretically in order to find some potential radical precursors or probes for hydroxyl radical reactions with aromatics.; To avoid the problems typically encountered in the measurement of rate constants of O2·- trapping by nitrones, a more straightforward approach, stopped-flow UV methodology, has been developed in our study using KO2 as a direct source of O2 ·-. The absolute rate constants for the reactions of superoxide radical anion with five different spin traps were measured experimentally.; The conformational and IR spectroscopic studies of several novel capsules were studied computationally. The theoretical data rationalized the experimental results, and demonstrated, along with experimental data, that these compounds have a tendency to associate intramolecularly. The conformational dynamics and thermodynamics of a series of monovalent ureas, the synthetic divalent urea and its dimer were computationally studied using the B3LYP/6-31+G** level of theory which was validated to be a suitable method to study this system.; Theoretical studies were also employed to study the radical-addition reactions of benzene with 13 radicals as well as regio- and diastereo-selectivity in the dimethyl dioxirane (DMDO) mediated epoxidation of carbohydrate-based oxepines.