Studies on Molecular Orbital Interaction in the Heteroatom System

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The present research proposal aims at the mechanistic studies of molecular orbital interactions in organic compounds containing heteroatom(s). The following three projects have been completed or partially completed.1. Studies of a weak interaction involving group-16 elementsWe have investigated the nature of two weak interactions, i.e. hydrogen bonds involving group-16 elements and Se・・・N non-bonded attractive interaction. In general, hydrogen bonds are formed by electrostatic attractive forces between electronegative elements. However spectroscopic studies on the hydrogen bonding system X・・・H-Y(X=O, S, Se, Te and Y=O, C) have revealed that orbital interaction seems important in heavy heteroatom systems. In particular, it has been found that there exists fairly strong Se・・・H-C hydrogen bond, in which electrostatic attraction is not expected Se・・・N non-bonded attractive interaction(J.Am.Chem, Soc., 116, 1994 in press as a short communication). Se・・・N non-bonded attractive interaction ha … More s also been studied both experimental and theoretical point of view. It was found that this interaction is not an electrostatic one either(J.Am.Chem, Soc., submitted).2. Importance of orbital interaction in glutathione peroxidase catalytic cycleGlutathione peroxidase is a poly peptide enzyme which reduces hydrogen peroxide generated as a metabolite of active oxygen in animals. Its active center contains a selenium atom that is surrounded by two nitrogen atoms of amino acid residues. The plausible roles of these proximate nitrogen atoms on the catalytic cycle have been studied using a simple model compound containing a selenium and a proximate tertiary amino nitrogen. This work will appear in J.Am.Chem, Soc., 116, 1994 as a full paper.3. Studies on the selectivities of organic reactionsTwo projects have been completed. One concerns with the pi-facial stereoselectivity of hydride reduction of cyclic ketones(J.Am.Chem, Soc., submitted) and the other is the regioselectivity in the Sn2 reaction of heteroatom-substituted epoxides. In both cases, LUMO extension outside repulsive molecular surface evaluated by "Exterior Electron Density" seems to play an important role on dictation of selectivities. Less