【作者】 宁洪岩； 杨丽； 张家旭；

【Author】 Hongyan Ning;Li Yang;Jiaxu Zhang;School of Chemistry and Chemical Engineering, Harbin Institute of Technology;

【机构】 哈尔滨工业大学化工与化学学院；

【摘要】 本文使用MP2和多种密度泛函方法B3LYP,B97-1,BhandH,M06和CAM-B3LYP,结合ECP/d基组,分别研究了气相反应F^-+（CH₃）₂CHI和F^-+（CH₃）₃CI两个体系的势能曲线。对于F^-+（CH₃）₂CHI反应,基于MP2/ECP/d优化的几何结构,在更高理论水平CCSD（T）/PP/t下进行单点能量计算,作为评估方法准确性的参考值。两个体系均有三种不同的反应通道,分别为S_N2,anti-E2和syn-E2,并且每种反应通道的势能面均呈现"双势阱"特征。研究发现随着α碳上甲基取代的增加,S_N2反应的势垒显著增加（4.5kcal/mol在M06水平下）,而E₂反应的势垒只是略有增加（在M06水平下anti-E2和syn-E2通道中势垒分别增加了0.8和0.7kcal/mol）。每一个反应体系中,E2的过渡态几何构型与S_N2不同。Anti-E2和syn-E2通道中的过渡态几何构型相似,但根据势垒分析anti-E2消除反应更易进行。对于两个体系,anti-E2和S_N2均为主要的竞争通道。计算结果表明,F^-+（CH₃）₂CHI体系中M06/ECP/d水平下的能量与CCSD（T）符合最好,因此,该方法将被选作执行直接动力学模拟。更多还原

【Abstract】 For the gas-phase reactions of F with（CH₃）₂CHI and（CH₃）₃CI,S_N2,anti-E2,and syn-E2 reaction paths were investigated by applying MP2 and DFT theories and found that the reactions proceed via a double-well potential.In this work,the addition of a methyl group at the α-carbon increases the S_N2 barrier（by 4.5kcal/mol at M06 level）,yet it augments slightly the E2 barriers（0.8 and 0.7kcal/mol for anti and syn mechanisms,respectively）.For both systems,the geometry of the E2 TS is shown to be entirely different from that of the S_N2 TS.Although the TS geometries of the anti-and syn-E2 reactions are similar,the anti-E2 is significantly favored over the syn-E2 according to the barrier.A comparison of the energetics of the S_N2 and E2 reactions predicts that elimination will dominate in two systems.The calculations reported here suggest that M06 is the preferred method for direct dynamics simulations.更多还原