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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Isomerization barriers for the disrotatory and con rotatory isomerizations of 3-aza-benzvalene and 3,4-diaza-benzvalene to pyridine and pyridazine
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Isomerization barriers for the disrotatory and con rotatory isomerizations of 3-aza-benzvalene and 3,4-diaza-benzvalene to pyridine and pyridazine

机译：3-氮杂-苯并戊环和3,4-二氮杂-苯并戊环向吡啶和哒嗪的旋转异构和旋转异构的异构化障碍

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摘要

The isomerizations of 3-aza-benzvalene to pyridine and 3,4-diaza-benzvalene to pyridazine have been studied using ab initio methods with a multiconfigurational wavefunction. Transition states for both the allowed disrotatory and forbidden conrotatory pathways were located. The forbidden pathways proceed through an intermediate consisting of pyridine or pyridazine with a trans double bond in the ring: this trans double bond destroys the aromatic stabilization of the n electrons due to poor orbital overlap between the cis and trans n bonds. Due to the C_s molecular point group, there are two separate allowed and forbidden pathways for 3-aza-benzvalene. The separation of the barrier heights was of particular interest: the difference in activation barriers for the lowest allowed and lowest forbidden pathways in 3-aza-benzvalene was only 1.3 kcal mol~(-1), and the lowest forbidden pathway actually had a 1.5 kcal mol~(-1) lower barrier than the highest allowed one. The 3-aza-benzvalene structure allows energy crossing of the allowed and forbidden barriers. For 3,4-diaza-benzvalene, there was only a single allowed and single forbidden pathway, due to the C_(2v) point group, and they were separated by 8.4 kcal mol~(-1), more in line with the orbital symmetry rules.
机译：已使用具有多种构型波函数的从头算方法研究了3-氮杂-苯并戊环向吡啶的异构化和3,4-二氮杂-苯并戊环向哒嗪的异构化。确定了允许的旋转路径和禁止的旋转路径的过渡状态。禁止的途径通过由吡啶或哒嗪组成的中间体，该中间体在环中具有反式双键：由于顺式和反式n键之间的轨道重叠差，该反式双键破坏了n电子的芳族稳定作用。由于C_s分子点基团的存在，3-氮杂-苯并戊烯有两个单独的允许和禁止途径。势垒高度的分离特别令人关注：3-氮杂-苯并戊烯中最低允许途径和最低禁止途径的激活势垒之差仅为1.3 kcal mol〜（-1），最低禁止途径实际上具有1.5 kcal mol〜（-1）。 kcal mol〜（-1）的势垒比允许的最大值低。 3-氮杂-苯并戊烯结构允许能量越过允许和禁止的势垒。对于3,4-二氮杂-苯并戊烯，由于存在C_（2v）点群，只有一个允许和禁止的途径，它们之间的间隔为8.4 kcal mol〜（-1），与轨道更一致对称规则。

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