theoretical calculations predicted a very weak C–C bond with a bondlength around 1.8 Å. This bond is expanded by the forced adoption of an eclipsed conformation and by angle strain through a “scissor effect.” The highly strained hydrocarbon was isolated as a thermally stable compound with no signs of diradical contribution because the weak C–C bond (core) is protected by the shape-persistent fused-ring
基于分子内“核-壳策略”,我们设计了带有两个螺环(二苯并环庚三烯)单元的二氢次萘,理论计算结果表明,该键具有很弱的C–C键,键长约为1.8Å。通过强制采用暗淡的构象以及通过“剪刀效应”引起的角度应变,可以扩大这种结合。高应变烃是一种热稳定的化合物,没有任何自由基的迹象,因为弱的C–C键(核)受到形状持久的稠环结构(壳)的保护。对应于C–C拉伸振动(587 cm -1)的拉曼位移与乙烷(993 cm -1)的拉曼位移非常不同)。通过X射线测定的键长(1.806(2)Å)大于最短的非键分子内C … C接触(1.80(2)Å)。通过假设键长与共价键的键解离能之间呈线性相关,假定的C–C键极限(1.803Å)是无效的。
Flexible C−C Bonds: Reversible Expansion, Contraction, Formation, and Scission of Extremely Elongated Single Bonds
Since carbon–carbon (C−C) covalent bonds are rigid and robust, the bond length is, in general, nearly constant and depends only on the bond order and hybrid orbitals. We report herein direct visualization of the reversible expansion and contraction of a C(sp3)−C(sp3) single bond by light and heat. This flexibility of a C−Cbond was demonstrated by X‐ray analysis and Raman spectroscopy of hexaphenylethane