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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Solvation of the Menshutkin Reaction : A Rigorous Test of the Effective Fragment Method
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Solvation of the Menshutkin Reaction : A Rigorous Test of the Effective Fragment Method

机译：解决Menshutkin反应：有效片段法的严格测试

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摘要

The recently developed effective fragment potential (EFP) method is used to study the effect of two, four, six, and eight solvating water molecules on the Menshutking reaction between ammonia and methyl bromide. The EFP method reproduces all ab initio geometries and energetics (including zero-point energy, thermal, and entropy effects) for the two-water case very accurately. Energetics from all ab initio single-point energies at the EFP geometries for the four, six, and eight water cases are in excellent agreement with corresponding EFP energetics. in the gas phase, the above Menshutkin reaction is kinetically highly unfavorable with a free energy of activation (at 298.15 K) of 40.6 kcal/mol at the RHF level with a double-#zeta# basis set augmented with polarization and diffuse functions. An ion-pair product is found, in agreement with previous work, in which the bromide anion is hydrogen-bonded to an ammonium hydrogen, giving a free energy of reaction of 2.8 kcal/mol. The addition of solvating water molecules has the effect of lowering the barrier and lowering the energy of the ion-pair product relative to the molecule-pair reactant. For eight solvating EFP water molecules, the free energy of activation is 22.8 kcal/mol and the free energy of reaction is -21.9 kcal/mol. Timings indicate that the EFP method allows the inexpensive addition of water molecules to a chemical system, accurately modeling all ab initio calculations with low computational cost.
机译：最近开发的有效片段电势（EFP）方法用于研究两个，四个，六个和八个溶剂化水分子对氨和甲基溴之间的Menshutking反应的影响。 EFP方法可以非常精确地重现两水情况下的所有从头算起的几何形状和能量（包括零点能量，热和熵效应）。在四个，六个和八个水箱中，EFP几何结构的所有从头算起的单点能量的能量学与相应的EFP能量学非常吻合。在气相中，上述门舒特金反应在动力学上是非常不利的，在RHF水平具有40.6 kcal / mol的活化自由能（在298.15 K时），并带有极化和扩散功能增强的双zeta＃基。与先前的工作一致，发现了一种离子对产物，其中溴化物阴离子与氢铵形成氢键，反应自由能为2.8 kcal / mol。相对于分子对反应物，溶剂化水分子的添加具有降低势垒和降低离子对产物的能量的作用。对于八个溶剂化的EFP水分子，活化的自由能为22.8 kcal / mol，反应的自由能为-21.9 kcal / mol。时间表明EFP方法允许将水分子廉价地添加到化学系统中，从而以较低的计算成本准确地对所有从头算式进行建模。

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