Maulitz A H, Lightstone F C, Zheng Y J, Bruice T C
Department of Chemistry, University of California, Santa Barbara, CA 93106, USA.
Proc Natl Acad Sci U S A. 1997 Jun 24;94(13):6591-5. doi: 10.1073/pnas.94.13.6591.
The SN2 displacements of chloride ion from CH3Cl, C2H5Cl, and C2H4Cl2 by acetate and hydroxide ions have been investigated, using ab initio molecular orbital theory at the HF/6-31+G(d), MP2/6-31+G(d), and MP4/6-31+G(d) levels of theory. The central barriers (calculated from the initial ion-molecule complex) of the reactions, the differences of the overall reaction energies, and the geometries of the transition states are compared. Essential stereochemical changes before and after the displacement reactions are described for selected cases. The gas phase reactions of hydroxide with CH3Cl, C2H5Cl, and C2H4Cl2 have no overall barrier, but there is a small overall barrier for the reactions of acetate with CH3Cl, C2H5Cl, and C2H4Cl2. A self-consistent reaction field solvation model was used to examine the SN2 reactions between methyl chloride and hydroxide ion and between 1,2-dichloroethane and acetate in solution. As expected, the reactions in polar solvent have a large barrier. However, the transition state structures determined by ab initio calculations change only slightly in the presence of a highly polar solvent as compared with the gas phase. We also calibrated the PM3 method for future study of an enzymatic SN2 displacement of halogen.
利用从头算分子轨道理论，在HF/6 - 31 + G(d)、MP2/6 - 31 + G(d)和MP4/6 - 31 + G(d)理论水平下，研究了醋酸根离子和氢氧根离子对CH3Cl、C2H5Cl和C2H4Cl2中氯离子的SN2取代反应。比较了反应的中心势垒（由初始离子 - 分子复合物计算得出）、总反应能量的差异以及过渡态的几何结构。描述了选定情况下取代反应前后基本的立体化学变化。氢氧根与CH3Cl、C2H5Cl和C2H4Cl2的气相反应没有总势垒，但醋酸根与CH3Cl、C2H5Cl和C2H4Cl2的反应存在一个小的总势垒。使用自洽反应场溶剂化模型研究了溶液中甲基氯与氢氧根离子以及1,2 - 二氯乙烷与醋酸根之间的SN2反应。正如预期的那样，极性溶剂中的反应具有较大的势垒。然而，与气相相比，从头算计算确定的过渡态结构在高极性溶剂存在下仅略有变化。我们还校准了PM3方法，以便未来研究酶促SN2卤代取代反应。
