Rolf Huisgen explored the Diels–Alder reactions of 1,3,5‐cycloheptatriene (CHT) and cyclooctatetraene (COT) with the dienophiles maleic anhydride and 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione (PTAD) to determine the kinetics and mechanisms of various electrocyclizations and Diels–Alder reactions. These reactions have been examined with density functional theory. Modern computational chemistry has provided information not previously available by experiment. Transition states for all the reactions have been identified, and their Gibbs energies are used to explain the experimental reactivities. Zwitterionic intermediates were not found in the [4+2] cycloadditions of both CHT or COT with PTAD and are thus not involved in these reactions. [2+2+2] cycloadditions, as an alternative path to the Diels–Alder products, are highly disfavored. Rapid double nitrogen inversion was found for the cycloaddition products with PTAD.

中文翻译：

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罗尔夫·惠斯根（Rolf Huisgen）对环三烯Diels-Alder反应的经典研究，通过现代计算分析得到阐述。

罗尔夫·惠斯根（Rolf Huisgen）探索了1,3,5-环庚三烯（CHT）和环辛酸酯（COT）与亲二烯体马来酸酐和4-苯基-1,2,4-三唑啉-3,5-二酮（PTAD）的Diels-Alder反应确定各种电环化反应和Diels-Alder反应的动力学和机理。这些反应已经用密度泛函理论进行了检验。现代计算化学已经提供了以前无法通过实验获得的信息。已经确定了所有反应的过渡态，它们的吉布斯能被用来解释实验的反应性。在CHT或COT与PTAD的[4 + 2]环加成中均未发现两性离子中间体，因此不参与这些反应。[2 + 2 + 2]环加成作为Diels–Alder产品的替代途径非常不受欢迎。