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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >The Structrue of meta-Benzyne Revisited-A Close Look into #sigma#-Bond Formation
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The Structrue of meta-Benzyne Revisited-A Close Look into #sigma#-Bond Formation

机译：重述亚苄基的结构-仔细观察＃sigma＃-键形成

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A detailed density fuctional theory (DFT) and ab initio quantum chemical investigation of meta-benzyne (1) is presented with a focus on the distance of the racial centers C1 and C3. Energy profiles for the cyclization of the biradical form (1a) to give the highly strained bicyclic anti-Bredt olefin (1b) are calculated employing four different functionals (B3LYP, B3PW91, BLYP, BPW91) as well as different ab initio methods (HF, MP2, CASSCF) in combination with two different basis sets (cc-pVDZ, cc-pVTZ). To judge the performance of the different methods, high-level single-point calculations (CCSD(T)/cc-pVTZ, CASPT2/cc-pVTZ, and CAS(8,8)-CISD+Q/cc-pVTZ) are carried out for a large number of structures along the cyclization coordinate. These calculations show that only one minimum energy structure exists for meta-benzyne and that the C1C3 separation is 205 +- 5 pm. The topology of the PES as well as the equilibrium geometry strongly depend on the level of theory applied. Hybrid DFT methods overestimate bonding between the radical centers, pure GGA methods perform significantly better, and the BLYP fuctional appears to be the most suitable one for aromatic meta-biradicals. Despite the large distance of the radical centers in 1, the biradical character is low (19-32% depending on the definition of this quantity) and therefore neither 1a nor 1b is an appropriate representation of meta-benzyne. NBO population and topological analysis of the electron density distribution reveal that the best way to describe the electronic structure of this molecule is a #sigma#-allylic system in which primarily the antibonding C2H7 orbital participates in the interaction of the radical lobes.
机译：提出了详细的密度函数理论（DFT）和从头算量子化学研究间苯并（1），重点是种族中心C1和C3的距离。使用四种不同的官能团（B3LYP，B3PW91，BLYP，BPW91）以及不同的从头算方法（HF， MP2，CASSCF）与两个不同的基集（cc-pVDZ，cc-pVTZ）结合使用。为了判断不同方法的性能，进行了高级单点计算（CCSD（T）/ cc-pVTZ，CASPT2 / cc-pVTZ和CAS（8,8）-CISD + Q / cc-pVTZ）沿着环化坐标找出大量结构。这些计算表明，对间联苯只有一个最小的能量结构，C1C3的分离度为205±5 pm。 PES的拓扑以及平衡几何结构在很大程度上取决于所应用的理论水平。混合DFT方法高估了自由基中心之间的键合，纯GGA方法的效果明显更好，而BLYP功能似乎是最适合芳族双基自由基的方法。尽管自由基中心在1中相距很远，但双自由基特征仍然很低（取决于此量的定义，为19-32％），因此1a和1b都不是间苯并ben的适当表示。 NBO种群和电子密度分布的拓扑分析表明，描述此分子电子结构的最佳方法是＃sigma＃-烯丙基系统，其中主要的反键C2H7轨道参与自由基叶的相互作用。

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