Chen Zhongfang, Jiang De-en, Lu Xin, Bettinger Holger F, Dai Sheng, Schleyer Paul von Ragué, Houk Kendall N
Department of Chemistry and Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602, USA.
Org Lett. 2007 Dec 20;9(26):5449-52. doi: 10.1021/ol7023339. Epub 2007 Nov 29.
The electronic ground states of [n]cyclacenes, as well as short-zigzag nanotubes, computed at unrestricted broken spin-symmetry density functional theory (UBS-DFT), were found to be open-shell singlets, rather than triplets. Computations for [6]cyclacene at complete active space self-consistent field (CASSCF) and multireference perturbation theory (MRMP2) levels support this conclusion. Along with strain, the radical character of the open-shell singlet with antiferromagnetically coupled electron spins may contribute to the difficulties in synthesizing [n]cyclacenes.
在无限制破缺自旋对称密度泛函理论（UBS-DFT）下计算得到的[n]环并苯以及短锯齿形纳米管的电子基态，被发现是开壳层单重态，而非三重态。在完全活性空间自洽场（CASSCF）和多参考微扰理论（MRMP2）水平下对[6]环并苯的计算支持了这一结论。除了应变外，具有反铁磁耦合电子自旋的开壳层单重态的自由基特性可能导致[n]环并苯合成困难。
