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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >A Computational Study of the Structure and Synthesis of Formazans
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A Computational Study of the Structure and Synthesis of Formazans

机译：甲Structure的结构与合成的计算研究

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We report the results of a density functional theory (DFT) study of the structure and synthesis of a formazan molecule, 1,3,5-triphenylformazan. Three conformational minima of this formazan are identified, with the global minimum having an internal H-bond as part of a pseudo-six-membered ring. At the 6-31G(d) B3LYP level of theory the transition state for tautomerization and exchange of the hydrogen ion lies 4 kcal mol-1 above the global minimum. This barrier height is unchanged by the incorporation of solvent models. An extensive investigation of the potential energy surface for the synthesis of 1,3,5-triphenylformazan from benzaldehyde N-phenylhydrazone and benzenediazonium ion is reported. The results support the mechanism whose first step is the addition of the diazonium onto the central carbon atom of the phenylhydrazone. However, the transition states for both this addition and addition to the amino nitrogen atom lie on intrinsic reaction paths which connect to a minimum of the phenylhydrazone which is not its global minimum. The substitution of a methyl group for the hydrogen on the amino nitrogen of the hydrazone raises the energy of the initial intermediate by 10 kcal mol-1, preventing formazan formation. The increase in energy of the intermediate corresponds with an increase in energy (relative to that of the unmethylated case) necessary to place the benzaldehyde N-methyl-N-phenylhydrazone into the right conformation for reaction. The inclusion of a solvent model of ethanol made negligible difference to the computed geometric structures, but significant changes in energies relative to those of the reactants. However, adding self-consistent reaction field (SCRF) solvation energies to the gas-phase free energies gave relative values that were similar to those obtained by full inclusion of solvent effects (SCRF) in the optimization and vibrational frequency computations.
机译：我们报告了有关甲醛分子1,3,5-三苯基甲酰胺的结构和合成的密度泛函理论（DFT）研究的结果。确定了该甲an的三个构象极小值，整体最小值具有内部H键作为假六元环的一部分。在6-31G（d）B3LYP的理论水平上，互变异构和氢离子交换的过渡态高于全局最小值4 kcal mol-1。通过合并溶剂模型，该势垒高度不变。报道了对由苯甲醛N-苯基and和苯重氮离子合成1,3,5-三苯基甲酰胺的势能面的广泛研究。结果支持了该机理的第一步，该机理的第一步是将重氮盐加到苯hydr的中心碳原子上。但是，该加成和向氨基氮原子的加成的过渡态都位于固有的反应路径上，该路径与苯hydr的最小值相连，而不是其全局最小值。 of的氨基氮上的甲基被氢取代后，初始中间体的能量增加了10 kcal mol-1，从而防止了甲maz的形成。中间体能量的增加与将苯甲醛N-甲基-N-苯基phenyl置于正确的构象进行反应所需的能量增加（相对于未甲基化的情况）相对应。包含乙醇的溶剂模型对计算的几何结构的影响可忽略不计，但是相对于反应物的能量而言，能量发生了显着变化。但是，将自洽反应场（SCRF）溶剂化能量添加到气相自由能中得到的相对值类似于在优化和振动频率计算中完全包含溶剂效应（SCRF）所获得的相对值。

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