Mechanistic studies in carbene and polyurethane chemistry
The chemistry of benzylchlorocarbene was investigated through both theory and experiment. Photolysis of a phenanthrene-based precursor in an NMR tube gave evidence for isomeric beta-chlorostyrenes but not the alpha-isomer. Computations showed that insertion into the aromatic ring should have a barrier smaller than that for 1,2-hydrogen migration. Attempts were made to confirm the structure of a novel "ene" product that appears to result from addition of photogenerated cyclopentyne to cyclohexene. DFT calculations explored the energetics of these reactions and showed that Gilbert's bis-carbene mechanism is an unlikely route to the ene product. A variety of photochemical vinylidene precursors were prepared based on the phenanthrene and pyrene frameworks. Several substituted triazinanetriols were investigated and tested to determine catalytic ability and were successfully polymerized with difunctional isocyanates, p-tolyldiisocyanate (TDI) and poly-4,4 '-methylenebis(phenylisocyanate) (pMDI). Computational and NMR studies of a DABCO-isocyanate complex were performed and it was concluded that the equilibrium concentration of this complex was too low to measure. Preliminary results were acquired using a reaction calorimeter in the mechanistic studies of the reaction between an alcohol and an isocyanate. These results indicate that the reaction follows Farkas and Strohm's proposed mechanism and that the rate-determining step is the activation of the alcohol with an amine base. The lowest energy pathway for the interconversion of axial-methylcyclohexane to equatorial-methylcyclohexane was calculated at two Hartree-Fock levels of theory (HF/3-21G and HF/6-31G*) and at the Moller-Plesset level of theory (MP2/6-31G). Through the Hartree-Fock and Moller-Plesset levels of theory, we have determined that there is one lowest energy pathway for the interconversion of axial-methylcyclohexane to equatorial-methylcyclohexane. Calculations were attempted at a higher level of theory (density functional theory), however this level of theory caused the individual transition states to converge into one, not allowing us to determine a lowest energy pathway at that level of theory.*.
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