Theoretical Study Of Several Compounds About 4-acyl Pyrazolone

With the fast-growing development of computer technology and constantly updated theoretical methods, quantum chemistry calculation has become a powerful tool for exploring and analyzing problems of chemistry by the chemists. In order to gain a deeper insight into the photochromic property and coordinated property of 4-acyl pyrazolone compounds synthesized in our laboratory, the quantum chemical calculation has been performed. On the basis of previously experimental and theoretical work, G03 program package has been performed to investigate the photochromic mechanisms of 1, 3-diphenyl-4-(4-fluoro)benzal-5-pyrazoloneN(4)-phenyl semicarbazone (DP4FBP-PSC) and N-(1-phenyl-3-methyl-4-benzal-5-pyrazolone)-salicylidene (PMBP-SAL). Furthermore, we have studied the effect of halogen substituented in 4-acyl benzene on the photochromic properties of 1, 3-diphenyl-5-pyrazolone N(4)-phenyl semicarbazone (DPBP-PSC). The global and local indices have been calculated to assess the reactivity of N-(1-phenyl-3-methyl-4-propenylidene-5-pyrazolone)-salicylidene (PMPP-SAL).Chapter 1 provides theoretically studies on the geometrical properties, the nature of hydrogen bonds and photochromic mechanism of DP4FBP-PSC. The AIM theory has also been explored to analysis the strength of hydrogen bond existing in the crystal structure. Based on the AIM theory, the intermolecular O1-H???O2 hydrogen bonds are considered to be the strongest hydrogen bond which is compared favorably with the experimental result. By analyzing the connection of hydrogen bonds in the crystal structure of the title compound, a novel mechanism is proposed. The novel mechanism has different reaction pathway in the forward and the reverse process. That is, the forward direction has a great barrier and undergoes a multi-proton transfer, while the reverse direction has a small barrier and undergoes one proton transfer. This is in line with the experimental observations that the forward process needs irradiation of light while the reverse process will take place when heated.Chapter 2 mainly researches on the effect of halogen substituented in 4-acyl benzene on the photochromic properties of DPBP-PSC. The weaker the electron withdrawing ability of halogen atoms, the greater reactivity of studied isomers. The reactivity order that obtained from global indices is in line with the photoisomerization rate that obtained in laboratory, which suggests that the reactivity determines the photoisomerization rate. The calculated results also show that the reactivity of these isomers is enhanced when the hydrogen in 4-acyl benzene is stituented by halogen.Chapter 3 focuses on the structures, the nature of hydrogen bonds and the proposed photochromic mechanism of PMBP-SAL. The results show that the energies of keto form decrease from the gas phase to solvents, and the dipole moments of keto form have become greater in solvents. The stability of PMBP-SAL grows with the increase of solvent polarity. The geometrical parameters and stabilization energy E2 are applied to investigate the nature of hydrogen bond in the crystal structure. The results show that O3-H???O2 and N4-H???O1 are stronger hydrogen bonds. However, by analyzing several reaction paths, the double proton transfer reaction which through N4-H???O1 and N3-H???O2 is considered to be a favored process.Chapter 4 provides theoretically studies on the stability of PMPP-SAL both in the gas phase and ethanol solution, the global indices and the reactivity of selected atoms of studied isomers. Comparing study on the energies of these isomers shows that form I has the lowest enengy both in the gas phase and ethanol solution. It suggests that form I is the most stable isomer, which is in good agreement with experimental result. The calculated global indices indicate that form III and form II are the favorable isomers when reacts to mental ions because their reactivity is greater than that of form I. The condensed Fukui function, molecular electrostatic potential and selected atom orbitals percentage of the frontier orbital compositions predict that O1, O2, N2 and N3 are the most favorable atomic sites for electrophilic attack in form II- and III2-. Because of the position in the molecule, N2 usually adopts a bridge coordination mode connecting metal ions.