Department of Chemistry and Biochemistry, ‡Department of Chemical and Biomolecular Engineering, University of California , Los Angeles, California 90095, United States.
J Am Chem Soc. 2016 Feb 10;138(5):1660-7. doi: 10.1021/jacs.5b12054. Epub 2016 Feb 2.
The cycloadditions of benzene and ten different azabenzenes (pyridine, three diazines, three triazines, and three tetrazines) with the ethylene dienophile have been explored with density functional theory (M06-2X) and analyzed with the distortion/interaction model. Activation barriers correlate closely with both distortion energies and interaction energies over an activation energy range of 45 kcal/mol. The replacement of CH with N increases Diels-Alder reactivity due not only to the more favorable orbital interaction, but also to a decrease in distortion energy. The rates of reactions are greatly influenced by the nature of the bonds being formed: two C-C bonds > one C-C bond, and one C-N bond > two C-N bonds. The activation energy of Diels-Alder reactions correlates very well with reaction energies and with the NICS(0) values of the aromatic dienes. The distortion energy of the Diels-Alder reaction transition states mostly arises from the diene out-of-plane distortion energy.
用密度泛函理论（M06-2X）研究了苯和十种不同的氮杂苯（吡啶、三种二嗪、三种三嗪和三种四嗪）与乙烯二烯亲二烯体的环加成反应，并通过扭曲/相互作用模型进行了分析。在 45 kcal/mol 的活化能范围内，活化能与变形能和相互作用能密切相关。用 N 取代 CH 不仅由于更有利的轨道相互作用，而且由于变形能降低，增加了 Diels-Alder 反应性。反应速率受形成键的性质的极大影响：两个 C-C 键>一个 C-C 键，一个 C-N 键>两个 C-N 键。Diels-Alder 反应的活化能与反应能和芳香二烯的 NICS(0)值非常相关。Diels-Alder 反应过渡态的变形能主要来自二烯的非平面变形能。
