Theory Study On The Mechanisms Of Two Organic Reactions, Theoretical Simulation Of Ultraviolet Absorption Spectrum

Organic synthesis reactions have brought earthshaking changes to human life in the area of medicine, chemical industry and agriculture. Mechanism of an organic reaction can help us to explain the experimental phenomena, verify experimental results, and predict the new reactions.In this thesis, we firstly use density functional theory(DFT) to study reaction mechanisms of two organic reactions( "amino acid dehydration condensation reaction to form cyclic dipeptides" and "triphenylphosphine–catalyzed the reaction of allenoate with aimine for the synthesis of α,β-unsaturatedγ-carbon-amino ester"). Secondly, a series of cooper complex ultraviolet absorption spectra are simulated by using different functionals, and then compare computational results with the experimental.Chapters 1 and 2 give brief introductions on the cyclic dipeptide, organophosphone acting as a catalyst, and the adopted theoretical methods in this thesis. In chapter 3, we mainly study the amino acid dehydration condensation reaction mechanism of cyclic dipeptide, and reaction process that nine different amino acids dehydrate to form cyclic dipeptides. Chaper 4 mainly studies the triphenylphosphine as a catalyst to catalyze the reaction of allenoate for the synthesis of α,β-unsaturated carbon-γ-amino ester compounds. thermodynamic and kinetic aspects explain the stereoselectivity of reaction product, this new reaction mechanism will provide the theoretical reference data for synthesis of γ- amino esters. Chapter 5 from the theoretical simulation of a series of copper complex ultraviolet absorption spectrum, and comparison with the experiment results, draw a valuable conclusions.1. Amino acid dehydration condensation reaction mechanism of cyclic dipeptide. Firstly, reports on the basis of the experiment, we speculated three possible reaction pathways(Path 1,Path 2 and Path 3). All geometries of reactants, precursors, products and transition states(TS) were fully optimized at the M06-2X/6-311++G(d, p) level of theory, with water as solvent in IEFPCM solvation model. The frequency calculations were carried out at the same level to verify the optimized structures to be energy minima without any imaginary frequency, whereas transition states have one and only one imaginary frequency. Based on the research of the calculation results and comparison, it is conclude that the energetic favorable is Path 3. In addition, reaction process that nine different amino acids dehydrate to form cyclic dipeptides was also simulated to give the impact that hydrophilic and hydrophobic of R groups have on the reaction energy barriers. This work provides important theoretical reference for the study of analogous reaction mechanisms and development of more efficient catalysts2. Triphenylphosphine catalyzes to synthesis α,β-unsaturated carbon γ-amino esters. The mechanisms of PPh3-catalyzed to synthesis α, β- unsaturated γ-carbonamino esters using DFT. According to the experimental results, three possible reaction pathways(Path A1, Path A2 and Path A3) were proposed. There reaction paths of all geometries of reactants, precursors, products and transition states(TS) were fully optimized at the M06-2X/6-31G(d, p) level of theory, with diethyl ether as solvent in IEFPCM solvation model, and the frequency calculations were carried out at the same level. Finally, the structural basis that has been optimized can be calculated about single point energy in the level of M06-2X/6-311G(d, p). Analysis results show that Path A2 dominate the reaction channel of energy. At the same time, we also considered the reaction R1 trans-configuration, have three possible reaction pathways(Path B1, Path B2 and Path B3). The calculation results show that Path B2 dominate the reaction channel of energy. This new reaction mechanism research from two aspects of thermodynamic and kinetic aspects explain the stereoselectivity of reaction product, as well as provide the theoretical reference data for synthesis of γ-amino esters.3. Theoretical simulation about ultraviolet absorption spectrum of a series of metal copper complex. First of all, copper complex optimization fully optimized use B3 LYP, M06-2X and M06-L method. Then, based on The Time-dependent Density Functional Theory(TD-DFT) under the corresponding condition, complex electron energy from the singlet state to the excited state and the shock intensity were calculated. Finally, the experimental spectra were compared and analyzed with spectra from calculated data. A large number of theoretical calculations and statistical comparisons come to conclusion that has similar molecular structure to complexes F, G. Copper atoms should use LanL2 DZ base set, other atoms should use 6-311++G(d, p) basis set. This work also requires theoretical simulation and further statistics of a large amount of complexes.