| Kinetic studies of the hydride transfer systems in acetonitrile were carried out to test the concept of the isotopically different tunneling-ready-state (TRS) structures in which deuterium (D)-tunneling has shorter donor-acceptor distance (DAD) than protium (H)-tunneling. The hydride transfer reactions include the reactions between 1-phenylethanol and 9-phenylxanthylium ion (PhXn +) and between 9-phenyl Hantzsch ester (PhHEH) and para-substituted-9-phenyl derivative of PhXn+ (p-GPhXn+ (G = CH3 O, H and Cl). The primary isotope effect on secondary kinetic isotope effects (KIEs) and Hammett correlations were determined to study differences in conformational and electronic structure of the tunneling ready state (TRSs) of the H- and D-tunneling processes. Results indicate that there is no significant steric interaction between the CH3/D3 groups in 1-phenylethanol and any moieties of the PhXn+ in the TRS of the former reaction, but the electronic structures of the H- and D-tunneling TRSs of the latter series of reactions are different. |
