Mechanism of organic reaction in solution : kinetics experiment and new QM/MM computations

点击翻译按钮获取中文摘要

Computational study with a QM/MM method has been carried out for S_N1-S_N2 reactions of alkyl halides in water, and the effect of solvent on the reaction pathways and the transition state structures was analyzed. The results were presented in domestic and oversea meetings. We are currently studying organic reactions in solution with Fragment MO(FMO) method as well.Activation and reaction energies were calculated for acid-base reactions of nitromethane, nitroethane, and substituted phenyllnitromethanes in the gas phase, water-solvated cluster, and solution systems. The experimentally observed nitroalkane anomaly in the proton-transfer rate-equilibrium correlation for the nitromethane and nitroethane systems was reproduced in solution but not in the gas phase. The origin of the anomaly was analyzed, and the importance of solvation was demonstrated. However, the anomaly in the Bronsted correlation for the arylnitromethane system could not be reproduced computationally even in solution. We plan to elucidate this problem by using QM/MM and FMO methods.Kinetic study was carried out for the carbonyl addition reactions. Stopped-flow experiment for the reactions of substituted benzaldehyde and benzopohenones with RLi and RMgX revealed that these reagents exist as aggregates (tetramer or dimer) and react as monomers. Other basic organic reactions such as molecular rearrangements and keto-enol isomerizations were studied both experimentally and computationally.