Study of the Isotopically Different Tunneling-Ready-State Electronic Structures in Hydrideversus Deuteride-Transfer Reactions

• Main Author: Salimraftar, Nasim
• Language: EN
• Published: Southern Illinois University at Edwardsville 2018
• Subjects: Biochemistry
• Online Access: http://pqdtopen.proquest.com/#viewpdf?dispub=10815604

<p> 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 (<i> G</i>-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&rsquo;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&deg;) H isotope substitution with D affects the kinetic isotope effect (KIE) at the in-place secondary 2&deg; H/D positions (2&deg; 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&deg; isotope dependence of 2&deg; KIEs in hydride transfer reactions to differentiate the isotopically different TRS conformations. It has been revealed that the 1&deg; isotope dependence of the 2&deg; KIEs is increased by the steric effects supporting the assumption of different DADs in H- <i>versus </i> D-tunneling, which leads to the different conformations of TRS. My approach in this research is focused on the study of 1&deg; isotope effect on the Hammett correlations at the <i>G</i>-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 <b>(&rho;H - &rho;D &ne; 0)</b> for the corresponding Hammett correlations.</p><p>