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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Comparative studies on the reactions of acetyl and thioacetyl halides with NH3 in the gas phase and in aqueous solution: A theoretical study
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Comparative studies on the reactions of acetyl and thioacetyl halides with NH3 in the gas phase and in aqueous solution: A theoretical study

机译：乙酰基和硫代乙酰卤化物与NH 3在气相和水溶液中反应的比较研究：理论研究

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摘要

The reactions of acetyl halides, CH_3C(=O)X and corresponding sulfur analogues, thioacetyl halides, CH_3C(=S)X, where X = F and Cl, with NH_3 nucleophile were studied theoretically, at the QCISD level of theory, in the gas phase and in aqueous solution. All reactions occurred via the tetrahedral species, and reactions through neutral intermediates both in the gas phase and in aqueous solution could be ruled out, except for the case of the gas-phase reaction of acetyl fluoride. The tetrahedral structure was a transition state (TS) in the reactions of acetyl chloride, while it was a stable intermediate in reactions of thioacetyl halides. These differences could be caused by the π-bond strength of C=O and C=S. In the case of acetyl fluoride, the T~±-type species was neither a saddle point nor an energy minimum in the gas phase, but existed as a stable intermediate in aqueous solution due to solvation. Moreover, in reactions of thioacetyl chloride, the rate-limiting step changed from the first step in the gas phase to the second step in aqueous solution, since the zwitterionic intermediates become more stabilized in aqueous solution. However, lower activation energies (ΔG~1) in aqueous solution were not caused by the solvent effects, but smaller deformation effects, in going from reactants through the TS.
机译：在QCISD的理论水平上，理论研究了乙酰卤化物CH_3C（= O）X和相应的硫类似物硫代乙酰卤化物CH_3C（= S）X（其中X = F和Cl）与NH_3亲核试剂的反应。气相和水溶液中。所有反应均通过四面体物种进行，并且可以排除在气相和水溶液中均通过中性中间体进行的反应，但乙酰氟的气相反应除外。在乙酰氯的反应中，四面体结构是过渡态（TS），而在硫代乙酰卤化物的反应中，四面体结构是稳定的中间体。这些差异可能是由C = O和C = S的π键强度引起的。在乙酰氟的情况下，T〜±型物质既不是鞍点也不是气相中的能量最小，而是由于溶剂化而作为稳定的中间体存在于水溶液中。此外，在硫代乙酰氯的反应中，由于两性离子中间体在水溶液中变得更稳定，所以限速步骤从气相中的第一步改变为水溶液中的第二步。然而，水溶液中较低的活化能（ΔG〜1）不是由溶剂效应引起的，而是由反应物穿过TS引起的较小的变形效应。

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