Combined molecular mechanical and quantum mechanical potential study of a nucleophilic addition reaction in solution
Combined molecular mechanical and quantum mechanical potential study of a nucleophilic addition reaction in solution
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溶液中亲核加成反应的分子力学和量子力学势组合研究
DOI：
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发表时间：
1994
影响因子：
3
通讯作者：
Yunyu Shi
中科院分区：
文献类型：
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作者：
Haiyan Liu;Yunyu Shi
采用半经验量子力学（AM 1）和分子力学势（7）相结合的方法研究了溶液中氢氧化物与甲醛的亲核加成反应。气相AM 1势面比相应的从头算6 - 31 + G* 计算结果多放热约26 kcal/mol。通过分子动力学模拟确定了溶液中反应的自由能分布。所得活化自由能约为5 kcal/mol。反应物和产物的溶剂化自由能之差约为38 kcal/mol。随着反应的进行，氢氧化物氧与周围水分子形成的氢键数量减少，而羰基氧形成的氢键数量增加。在整个反应过程中，溶质和溶剂分子之间的氢键总数没有明显的变化，这些氢键的平均数在5到6之间。这些结果与先前使用基于气相从头算6 - 31 + G* 计算的模型的研究一致。溶液中的反应路径与气相中的最小能量反应路径不同，当两种反应物相距较远时，溶液中氢氧根离子的进攻路径接近垂直于甲醛平面，而气相中氢氧根离子的进攻路径与羰基平面共线。这些结果表明，虽然AM 1不产生准确的能量在气相中，有价值的见解溶剂的影响，可以通过计算机模拟与此结合的潜力。这种结合的过程可以应用于大分子内的化学反应，其中环境影响的定量估计不容易通过另一种技术实现。© 1994年由John Wiley & Sons，Inc.
The procedure of combined semiempirical quantum mechanical (AM1) and molecular mechanical potential7 was used to study the nucleophilic addition of hydroxide to formaldehyde in solution. The gas phase AM1 potential surface is approximately 26 kcal/mol more exothermic than the corresponding ab initio 6‐31 + G* calculation results. The free energy profile for the reaction in solution was determined by means of molecular dynamic simulations. The resulting free energy of activation is approximately 5 kcal/mol. The difference of the free energy of solvation between the reactant and the product states is about 38 kcal/mol. As the reaction goes on, the number of hydrogen bonds formed by the hydroxide oxygen with the surrounding water molecules decreases, whereas the number of hydrogen bonds formed by the carbonyl oxygen increases. There is no significant change in the total number of hydrogen bonds between the solute and the solvent molecules, and the average number of these hydrogen bonds is between five and six during the entire reaction process. These results are consistent with previous studies using a model based on ad initio 6‐31 + G* calculations in the gas phase. The reaction path in solution is different from the gas phase minimum energy reaction path. When the two reactants are at a large distance, the attack route of the hydroxide anion in solution is close to perpendicular to the formaldehyde plane, whereas in the gas phase the route is collinear with the carbonyl group. These results suggests that although AM1 does not yield accurate energies in the gas phase, valuable insights into the solvent effects can be obtained through computer simulations with this combined potential. This combined procedure could be applied to chemical reactions within macromolecules, in which a quantitative estimation of the effects of the environment would not be easily attainable by another technique. © 1994 by John Wiley & Sons, Inc.