Development of New Frontier Orbital Theory

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To control the selectivity in synthetic processes and to design novel reagents and catalysts, the basic theory in chemistry of general use, having high applicability and clarity is needed. In the old frontier orbital theory, a single orbital delocalized over the whole molecular framework is utilized to discuss the reactivity of molecules. As a result, it cannot provide us with reliable information when we deal with sizable systems. In this research, we have developed a new orbital interaction theory on the basis of the paired interaction orbital scheme and the projected reactive orbital method, explored by us. The new theory has been demonstrated to be extremely useful in clarifying the electronic mechanism of chemical reactions and in predicting the reactivity of molecules. The characteristics of a variety of chemical reactions can be represented in terms of amplitude and phase of interacting orbitals in each system. The hardness of the reaction site as a Lewis acid or a Lewis base ha … More s been formulated in terms of local electron-accepting or -donating ability and chemical hardness of the reaction site, and has been estimated numerically in molecular orbital calculations. The effects of substituent groups on the acid-base property in aminoboranes, and the factors that control the endo selectivity in the Diels-Alder reaction between cyclopropene and several substituted butadienes have been disclosed. It has been demonstrated that the concept of secondary orbital interactions that has been used frequently in literature for more than thirtyfive years lacks in a sound theoretical base. We have clarified next the electronic mechanism of activation of oxirane by biphenylenediol and the orbital interaction that brings an anomeric effect to saturated systems. The reaction paths of palladation of methylenecyclopropane and [3 + 2] addition to alkenes and of intramolecular rearrangements in ruthenium and iron dihydrides have been analyzed. The site selectivity in self-assembling of thiol monolayer on the gold surface has also been discussed by utilizing the theoretical method developed in this research. The effect of water as a solvent in chemical reactions has been studied by means of quantum chemical calculations, in collaboration with an experimental research group. Less