Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
J Org Chem. 2012 Sep 7;77(17):7612-9. doi: 10.1021/jo3016105. Epub 2012 Aug 24.
Stretch effects induced by two types of molecular strain were examined by quantum chemical calculations at the B3LYP/6-31G(d), B3LYP/cc-PVDZ, CCSD/6-31G(d), and CASPT2/ANO-RCC-VTZP level of theory, to design persistent multiradicals such as localized diradicals and oxyallyls. The cooperative molecular strain (Type-1) induced by the spiro[5.5]undecane and bicyclo[2.1.0]cyclopentane structures was found to significantly destabilize in energy the ring-closed compounds of the diradicals, leading to small energy differences between the diradicals and the σ-bonded compounds. Another stretch effect (Type-2) induced by macrocyclic systems was also found to energetically destabilize the corresponding ring-closed structures of the 1,3-diradicals. The computational studies predict that the two types of stretch effects are quite effective in lowering the energy barriers of the bond-breaking reaction of the ring-closed compounds and in generating long-lived localized diradicals and oxyallyl derivatives.
通过量子化学计算在 B3LYP/6-31G(d)、B3LYP/cc-PVDZ、CCSD/6-31G(d) 和 CASPT2/ANO-RCC-VTZP 理论水平上研究了两种类型的分子应变引起的拉伸效应，以设计持久的多自由基，如局域双自由基和氧杂环丙烯。发现螺[5.5]十一烷和双环[2.1.0]环戊烷结构引起的协同分子应变（Type-1）显著降低了双自由基的环闭化合物的能量，导致双自由基和 σ 键合化合物之间的能量差异很小。还发现由大环系统引起的另一种拉伸效应（Type-2）也会使相应的 1,3-双自由基的环闭结构在能量上不稳定。计算研究预测，这两种拉伸效应在降低环闭化合物的键断裂反应的能垒和生成长寿命局域双自由基和氧杂环丙烯衍生物方面非常有效。
