Crystal Structure Determination of the Nonclassical 2-Norbornyl Cation
Crystal Structure Determination of the Nonclassical 2-Norbornyl Cation
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DOI：
10.1126/science.1238849
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发表时间：
2013-07-05
期刊：
影响因子：
56.9
通讯作者：
Krossing, I.
中科院分区：
文献类型：
--
作者：
Scholz, F.;Himmel, D.;Krossing, I.
在对2-降冰片基阳离子的经典或非经典结构进行了数十年的激烈争论之后，人们终于在溶剂化的[C7H11](+)[(AlBr7)- br -2]（-）中心点CH2Br2盐中实现了这种原型碳离子桥接的非经典几何结构的x射线晶体学证明。这一成就需要特殊的待遇。在CH2Br2中，降冰片基溴与三溴化铝反应得到的晶体由于2-降冰片基阳离子部分内部6,1,2-氢化物的移位，在86开尔文时发生了可逆的有序-无序相变。经过仔细的退火冷却，得到了一个适当有序的相。在40开尔文的温度下收集数据并进行精化，发现三个独立的2-降冰片基阳离子在单位细胞中具有相似的分子结构。这三种结构都与MP2(FC)/def2-QZVPP理论水平上的量子化学计算非常吻合。
After decades of vituperative debate over the classical or nonclassical structure of the 2-norbornyl cation, the long-sought x-ray crystallographic proof of the bridged, nonclassical geometry of this prototype carbonium ion in the solvated [C7H11](+)[(AlBr7)-Br-2](-)center dot CH2Br2 salt has finally been realized. This achievement required exceptional treatment. Crystals obtained by reacting norbornyl bromide with aluminum tribromide in CH2Br2 undergo a reversible order-disorder phase transition at 86 kelvin due to internal 6,1,2-hydride shifts of the 2-norbornyl cation moiety. Cooling with careful annealing gave a suitably ordered phase. Data collection at 40 kelvin and refinement revealed similar molecular structures of three independent 2-norbornyl cations in the unit cell. All three structures agree very well with quantum chemical calculations at the MP2(FC)/def2-QZVPP level of theory.