Department of Chemistry and Biochemistry, Swarthmore College , 500 College Avenue, Swarthmore, Pennsylvania 19081, United States.
J Org Chem. 2014 Feb 7;79(3):867-79. doi: 10.1021/jo4026644. Epub 2014 Jan 17.
High-level electronic structure calculations, including a continuum treatment of solvent, are employed to elucidate and quantify the effects of alkyl halide structure on the barriers of SN2 and E2 reactions. In cases where such comparisons are available, the results of these calculations show close agreement with solution experimental data. Structural factors investigated include α- and β-methylation, adjacency to unsaturated functionality (allyl, benzyl, propargyl, α to carbonyl), ring size, and α-halogenation and cyanation. While the influence of these factors on SN2 reactivity is mostly well-known, the present study attempts to provide a broad comparison of both SN2 and E2 reactivity across many cases using a single methodology, so as to quantify relative reactivity trends. Despite the fact that most organic chemistry textbooks say far more about how structure affects SN2 reactions than about how it affects E2 reactions, the latter are just as sensitive to structural variation as are the former. This sensitivity of E2 reactions to structure is often underappreciated.
采用包括溶剂连续体处理在内的高水平电子结构计算方法，阐明并量化了烷基卤化物结构对 SN2 和 E2 反应能垒的影响。在有此类比较的情况下，这些计算结果与溶液实验数据吻合较好。研究的结构因素包括α-和β-甲基化、与不饱和官能团（烯丙基、苄基、炔丙基、α-羰基）的相邻性、环大小以及α-卤化和氰化。虽然这些因素对 SN2 反应性的影响大多已为人所知，但本研究试图使用单一方法对许多情况下的 SN2 和 E2 反应性进行广泛比较，以量化相对反应性趋势。尽管大多数有机化学教科书在谈及结构如何影响 SN2 反应时远比谈论其如何影响 E2 反应要详细得多，但 E2 反应对结构变化的敏感程度与前者一样。E2 反应对结构的这种敏感性常常被低估。
