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首页> 外文期刊>Journal of Physical Organic Chemistry >Application of activation hardness in perturbed pericyclic reactions: A case study involving electrocyclic ring opening reactions of heterocyclobutenes
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Application of activation hardness in perturbed pericyclic reactions: A case study involving electrocyclic ring opening reactions of heterocyclobutenes

机译：活化硬度在扰动的环周反应中的应用：涉及杂环丁烯的电环开环反应的案例研究

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摘要

Cyclobutene undergoes electrocyclic ring opening through conrotatory mode to give 1,3-butadiene and similarly its skeletally substituted analogues viz. phosphetene, thietene, oxetene and azetene isomerize to give their respective heterodienes. Quantum mechanical investigations on these perturbed pericyclic isomerizations at B3LYP level with 6-31G(d) and 6-311 + G(d,p) basis sets reveal that hetero - atoms significantly lower the barrier and alter the reaction free energies. Interestingly frontier orbital correlation diagram shows that σ and σ* levels are perturbed significantly while π and π* levels undergo little changes during the reaction; the lone pairs on hetero - atoms are slightly stabilized in the TS. This results in σ becoming HOMO in the TSs of phosphetene and thietene isomerizations and σ* becoming LUMO in all the cases. This necessitates defining hardness values based on closely interacting frontier orbitals for reactants and TSs and use them to compute activation hardness values to interpret relative reactivity.
机译：环丁烯通过旋转方式经历环电开环，得到1,3-丁二烯及其类似物的骨架取代类似物。磷烯，硫杂环丁烯，氧杂环丁烯和氮杂环丁烯异构化以得到它们各自的杂二烯。在B3LYP水平上以6-31G（d）和6-311 + G（d，p）基集对这些扰动的周环异构化进行的量子力学研究表明，杂原子显着降低了势垒并改变了反应自由能。有趣的是，前沿轨道相关图显示，在反应过程中，σ和σ*能级受到显着扰动，而π和π*能级几乎没有变化。杂原子上的孤对在TS中略微稳定。这导致在所有情况下，在磷脂和硫杂环丁烯异构化的TS中σ变为HOMO，而σ*变为LUMO。这需要根据反应物和TS的紧密相互作用的边界轨道定义硬度值，并使用它们来计算活化硬度值以解释相对反应性。

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