Crystal Structure Determination of the Nonclassical 2-Norbornyl Cation

• DOI: 10.1126/science.1238849
• Publication Date: 2013-07-04T18:42:11Z
• Authors: F. Scholz; D. Himmel; F. W. Heinemann; P. v. R. Schleyer; K. Meyer; I. Krossing
• Keywords: 2-Norbornyl cation; Carbonium ion; Moiety; Markovnikov's rule

After decades of vituperative debate over the classical or nonclassical structure 2-norbornyl cation, long-sought x-ray crystallographic proof bridged, geometry this prototype carbonium ion in solvated [C7H11](+)[Al2Br7](-) • CH2Br2 salt has finally been realized. This achievement required exceptional treatment. Crystals obtained by reacting norbornyl bromide with aluminum tribromide undergo a reversible order-disorder phase transition at 86 kelvin due to internal 6,1,2-hydride shifts cation moiety. Cooling careful annealing gave suitably ordered phase. Data collection 40 and refinement revealed similar molecular structures three independent cations unit cell. All agree very well quantum chemical calculations MP2(FC)/def2-QZVPP level theory.