Theoretiacal Investigation On Organic Reaction And Organic Molecules-catalyzed Reaction Using DFT Methods

Theoretical studies were performed on five reaction systems with high stereo- and/or regio-selectivity. Particular attention was paid to the correlation between structures and their reactivities and the controlling factors of the selectivity for the reactions.The Diels-Alder (DA) reactions of various substituted ethenes (methyl vinyl ether (MVE), styrene and methyl vinyl ketone( MVK)) with ortho-Quinone methides(o-QM) are studied by means of the density functional theory (DFT) at the B3LYP/6-31G(d,p) level,there is relation between the nature of the molecular mechanism and the polar character of the substituted ethene, increasing the electron-releasing character of the substituent enhances the asynchronicity and the charge-transfer process as well as a significant decrease of the activation energy. The calculations also result that the solvent effects decrease the activation energy and increase the asynchronicity of these processes.The reaction mechanism of the L-proline-catalyzedα-aminoxylation reaction between aldehyde and nitrosobenzene has been investigated using density functional theory (DFT) calculation. The first step that corresponds to the formation of C-O bond is the stereocontrolling and rate-determining step. The intermolecular hydrogen-bond between the acidic hydrogen of L-proline and the N atom of the nitrosobenzene in an early stage of the process catalyzes very effectively the C-O bond-formation by a large stabilization of the negative charge that is developing at the O atom along the electrophilic attack. The effect of solvent decreases the activation energy, and also, the calculated energy barriers...