Ab initio molecular orbital calculations at the B3L YP/6-3l +G* and MP2/6-3l +G* levels have been performed to study the effect of microsolvation on the SN2 reaction profile for CI- + RCI (R = methyl, ethyl; i-propyl, and tert-butyl). Microsolvation corresponding to 0-4 water molecules, and 0-2 molecules of methanol, acetonitrile, acetone, dimethyl ether and propane has been investigated. The polarizable continuum solvent model has been used to investigate the effect of bulk solvation. The calculated barrier heights increase with the number of solvent molecules and the size of the R group. Microsolvation causes only small changes in the TS geometries for the methyl, ethyl, and i-propyl systems, whereas the tert-butyl TS becomes significantly looser. Microsolvation decreases the steric effect, with the modulation depending on the dielectric (;onstant of the solvent. For water, the decrease in steric effect is shown to be due to an increased solvation of the TS, mediated by the electron donating effect of the methyl group. The polarizable continuum solvent model in general underestimates changes in stericeffects due to solvation.
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机译：已经进行了B3L YP / 6-3l + G *和MP2 / 6-3l + G *一级的从头算分子轨道计算，以研究微溶剂化对CI- + RCI的SN2反应谱的影响（R =甲基，乙基;异丙基和叔丁基）。研究了对应于0-4个水分子以及0-2个甲醇，乙腈，丙酮，二甲醚和丙烷的微溶剂。可极化的连续介质溶剂模型已用于研究本体溶剂化的效果。计算的势垒高度随溶剂分子的数量和R基团的大小而增加。对于甲基，乙基和异丙基系统，微溶剂化仅会导致TS几何形状的微小变化，而叔丁基TS则明显变松。微溶剂化会降低空间效应，其调节取决于介电常数（溶剂的常数。对于水，空间效应的降低表明是由于甲基化的电子给体作用介导的TS溶剂化增加所致可极化连续介质溶剂模型通常会低估由于溶剂化引起的立体效应变化。
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