This research is aimed at understanding the quantum mechanical concept of the tunneling in hydride-transfer reactions in solution. The reaction is a redox reaction involving the hydride transfer from 2-propanol to a series of substituted carbocationic oxidizing agents, 9-arylxanthylium ions ( G-PhXn+), in acetonitrile. Explanations in the contemporary tunneling models utilize the concept of the longer donor-acceptor distance (DAD) at tunneling ready state (TRS) in protium (H)-tunneling as compared to deuterium (D)-tunneling. Our group’s hypothesis is that different DADs in H- vs. D-tunneling TRSs will lead to TRS conformations of different steric environment and possibly different electronic structures. This opens a new research direction that studies how primary (1°) H isotope substitution with D affects the kinetic isotope effect (KIE) at the in-place secondary 2° H/D positions (2° KIE) as well as the Hammett correlations. This dependence provides information about the structure of a TRS. Our group has previously conducted investigations on the structural effect on the 1° isotope dependence of 2° KIEs in hydride transfer reactions to differentiate the isotopically different TRS conformations. It has been revealed that the 1° isotope dependence of the 2° KIEs is increased by the steric effects supporting the assumption of different DADs in H- versus D-tunneling, which leads to the different conformations of TRS. My approach in this research is focused on the study of 1° isotope effect on the Hammett correlations at the G-PhXn+ to attempt to differentiate the isotopically different TRS electronic structures. The degree of electronic interactions between the neighboring groups from reactants is shown to vary from H- to D-tunneling reactions, suggesting different electronic structures of two isotopic TRSs. The evidence for this arises from the non-zero isotopic slope difference (ρH - ρD ≠ 0) for the corresponding Hammett correlations.
|Commitee:||De Meo, Cristina, Lu, Yun, Shabestary, Nahid|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 58/01M(E), Masters Abstracts International|
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