title: Crystal structure determination of the nonclassical 2-norbornyl cation.
abstract: 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](+)[Al2Br7](-) • 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.
authors.affiliation: Institut für Anorganische und Analytische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Scholz
authors.forename: D
authors.initials: D
authors.lastname: Himmel
authors.forename: F W
authors.initials: FW
authors.lastname: Heinemann
authors.forename: P v R
authors.initials: Pv
authors.lastname: Schleyer
authors.forename: K
authors.initials: K
authors.lastname: Meyer
authors.forename: I
authors.initials: I
authors.lastname: Krossing