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首页> 外文期刊>Chemistry: A European journal >Aromaticity effects on the profiles of the lowest triplet-state potential-energy surfaces for rotation about the C=C bonds of olefins with five-membered ring substituents: An example of the impact of Baird's rule
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Aromaticity effects on the profiles of the lowest triplet-state potential-energy surfaces for rotation about the C=C bonds of olefins with five-membered ring substituents: An example of the impact of Baird's rule

机译：芳香性对最低三重态势能表面旋转具有五元环取代基的烯烃的C = C键旋转的轮廓的影响：贝德法则的影响示例

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A density functional theory study on olefins with five-membered monocyclic 4n and 4n+2 π-electron substituents (C_4H_3X; X=CH ~+, SiH~+, BH, AlH, CH_2, SiH_2, O, S, NH, and CH~-) was performed to assess the connection between the degree of substituent (anti)aromaticity and the profile of the lowest triplet-state (T_1) potential-energy surface (PES) for twisting about olefinic C=C bonds. It exploited both Hückel's rule on aromaticity in the closed-shell singlet ground state (S_0) and Baird's rule on aromaticity in the lowest ππ* excited triplet state. The compounds CH_2=CH(C_4H_3X) were categorized as set A and set B olefins depending on which carbon atom (C2 or C3) of the C_4H _3X ring is bonded to the olefin. The degree of substituent (anti)aromaticity goes from strongly S0-antiaromatic/T _1-aromatic (C_5H_4 ~+) to strongly S_0-aromatic/T_1- antiaromatic (C_5H _4 ~-). Our hypothesis is that the shapes of the T _1 PESs, as given by the energy differences between planar and perpendicularly twisted olefin structures in T_1 [ΔE(T _1)], smoothly follow the changes in substituent (anti)aromaticity. Indeed, correlations between ΔE(T_1) and the (anti)aromaticity changes of the C_4H_3X groups, as measured by the zz-tensor component of the nucleus-independent chemical shift ΔNICS(T _1;1)_(zz), are found both for sets A and B separately (linear fits; r~2=0.949 and 0.851, respectively) and for the two sets combined (linear fit; r~2=0.851). For sets A and B combined, strong correlations are also found between ΔE(T_1) and the degree of S_0 (anti)aromaticity as determined by NICS(S_0,1) _(zz) (sigmoidal fit; r~2=0.963), as well as between the T_1 energies of the planar olefins and NICS(S_0,1) _(zz) (linear fit; r~2=0.939). Thus, careful tuning of substituent (anti)aromaticity allows for design of small olefins with T _1 PESs suitable for adiabatic Z/E photoisomerization.
机译：具有五元单环4n和4n + 2π电子取代基的烯烃的密度泛函理论研究（C_4H_3X; X = CH〜+，SiH〜+，BH，AlH，CH_2，SiH_2，O，S，NH和CH进行-（-）以评估取代基（反）芳族度和最低的三重态（T_1）势能表面（PES）的分布之间的联系，以扭转烯烃的C = C键。它既利用了Hückel关于闭壳单线态基态（S_0）的芳香性的规则，又利用了Baird关于最低ππ*激发三重态的芳香性的规则。化合物CH_2 = CH（C_4H_3X）分为A组和B组烯烃，具体取决于C_4H _3X环上的哪个碳原子（C2或C3）键合到烯烃上。取代基（抗）芳族度从强S 0-抗芳族/ T _1-芳族（C_5H_4〜+）变为强S_0-芳族/ T_1-抗芳族（C_5H _4〜-）。我们的假设是，T _1 PES的形状（由T_1中的平面和垂直扭曲的烯烃结构之间的能量差[ΔE（T _1）]所给定）平稳地遵循了取代基（抗）芳香性的变化。确实，发现ΔE（T_1）与C_4H_3X组的（反）芳香性变化之间的相关性，这是通过与核无关的化学位移ΔNICS（T _1; 1）_（zz）的zz张量分量测量的分别针对A和B组（线性拟合; r〜2 = 0.949和0.851），以及针对两组组合（线性拟合; r〜2 = 0.851）。对于组合的集合A和B，还发现ΔE（T_1）与S_0（反）芳烃度之间的强相关性，这由NICS（S_0,1）_（zz）确定（S型拟合; r〜2 = 0.963），以及平面烯烃的T_1能量与NICS（S_0,1）_（zz）之间（线性拟合; r〜2 = 0.939）。因此，仔细调节取代基（抗）芳构性可以设计出具有适合于绝热Z / E光异构化的T _1 PES的小烯烃。

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