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Catalysis Of The Aza-Diels-Alder Reaction By Hydrogen And Halogen Bonds, Vincent De Paul Nzuwah-Nziko, Steve Scheiner
Catalysis Of The Aza-Diels-Alder Reaction By Hydrogen And Halogen Bonds, Vincent De Paul Nzuwah-Nziko, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The combination of H2C=NH and cis-1,3-butadiene to form a six-membered ring was examined by quantum calculations. The energy barrier for this reaction is substantially lowered by the introduction of an imidazolium catalyst with either a H or halogen (X) atom in the 2-position, which acts via a H or halogen bond to the N atom of the imine, respectively. X=I has the largest effect, and Cl the smallest; Br and H are roughly equivalent. The catalyst retards the formation of the incipient N-C bond from imine to diene while simultaneously accelerating the C-C bond formation. The energy of the π* …
Building A Better Halide Receptor: Optimum Choice Of Spacer, Binding Unit, And Halosubstitution, Binod Nepal, Steve Scheiner
Building A Better Halide Receptor: Optimum Choice Of Spacer, Binding Unit, And Halosubstitution, Binod Nepal, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Quantum calculations are used to measure the binding of halides to a number of bipodal dicationic receptors, constructed as a pair of binding units separated by a spacer group. A number of variations are studied. A H atom on each binding unit (imidazolium or triazolium) is replaced by Br or I. Benzene, thiophene, carbazole, and dimethylnaphthalene are considered as spacer groups. Each receptor is paired with halides F-, Cl-, Br-, and I-. I-substitution on the binding unit yields a large enhancement of binding, as much as 13 orders of magnitude; a much smaller increase occurs for bromosubstitution. Imidazolium is a …