Ab initio study of the stability of [n]paracyclophanes and their Dewar benzene-type isomers
Ab initio study of the stability of [n]paracyclophanes and their Dewar benzene-type isomers
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[n]对环芳烷及其杜瓦苯型异构体稳定性的从头算研究
DOI：
10.1007/bf01374576
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
S. Peyerimhoff
中科院分区：
文献类型：
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作者：
M. Arnim;S. Peyerimhoff
对[n]副环烷及其杜瓦苯异构体形式=5、6和7，以及苯和杜瓦苯本身进行了初始计算。对苯的异构体进行了研究，采用了从6-31G型到3 -zeta型的各种AO基组合，包括碳上的二键和一键，氢上的二键和一键。采用MP2、CAS-SCF、MRD-CI和MCPF程序计算相关能贡献。在一定的几何假设下，计算了苯异构化过程中低能态的势曲线。计算出两个电位极值之间的能量差为3.35 eV；忽略电子相关使该值增加了约0.3 eV，极化描述的缺陷（6-31G基）又高估了0.65 eV。计算结果表明，实验杜瓦法测定苯的几何形状需要改进，六甲基苯的异构能比苯本身的异构能小得多。在6-31G的基础上，两种异构体形式的[n]副环番烯的几何形状都得到了优化；利用双zeta质量加偏振函数的AO基础来确定能量差。考虑了相关效应。未取代化合物的电子异构化能分别为2.58 eV （n=7）、1.63 eV （n=6）和0.7 eV （n=5）。用以苯环变形为“反应坐标”的势面图讨论了相对能量学。并与蒽异构化反应进行了比较，指出了取代基的影响。
Ab initiocalculations are carried out for [n]paracyclophanes and their Dewar benzene isomers forn=5, 6, and 7 as well as for the benzene and Dewar benzene itself. The benzene isomers are studied by employing various AO basis sets ranging from 6–31G type to such of triple-zeta type including twodand oneffunction on the carbons and twopand onedon the hydrogens. The correlation energy contribution is computed by employing MP2, CAS-SCF, MRD-CI and MCPF procedures. Potential curves for the low-energy states in the isomerization from benzene to its Dewar form are also computed under certain geometrical assumptions. The energy difference between the two potential minima is calculated to be 3.35 eV; neglect of electron correlation increases the value by about 0.3 eV, deficiencies in the polarization description (6-31G basis) overestimates it by another 0.65 eV. The calculations suggest that the experimental Dewar benzene geometry determination needs refinement and that the isomerization energy of hexamethylbenzene is considerably smaller than that of benzene itself.The geometries of the [n]paracyclophanes in both isomer forms are optimized in the 6-31G basis; the energy difference is determined by employing an AO basis of double-zeta quality plus polarization functions. Correlation effects are considered. The electronic isomerization energies are 2.58 eV (n=7), 1.63 eV (n=6) and 0.7 eV (n=5) for the unsubstituted compounds. The relative energetics are discussed in terms of potential surface diagram having the benzene ring deformation as the “reaction coordinate”. Comparison with the anthracene isomerization is made and the effect of substituents is pointed out.