X-ray Crystal Structures of a Benzonorbornenyl Cation and of a Protonated Benzonorbornenol<sup>†</sup>

2004-09-08T00:00:00Z (GMT) by Thomas Laube
The crystal structure of the 9-methylbenzonorbornenyl cation Me-<b>1</b><b><sup>+</sup></b><sup></sup> shows a relatively strong interaction between the sp<sup>2</sup>-hybridized carbon atom C9 and the aromatic ring (C4a−C9 ≡ C8a−C9 = 1.897(10) Å). The anion Sb<sub>2</sub>F<sub>11</sub><sup>-</sup> is refined as rotationally disordered along the Sb···Sb axis. In sharp contrast to the findings about Me-<b>1</b><b><sup>+</sup></b><sup></sup>, the protonated <i>anti</i>-benzonorbornenol <b>5</b><b><sup>+</sup></b><sup></sup> is essentially an oxonium ion with only weak interaction between the C9 bridge and the aromatic ring despite the fact that it is already a positively charged ion, which upon loss of a water molecule is expected to give the parent cation H-<b>1</b><b><sup>+</sup></b><sup></sup>. The hydrogen atoms on the oxonium O atom are involved in strong hydrogen bonds to chlorosulfonate anions and probably partially disordered despite the large estimated p<i>K</i><sub>a</sub> differences between the corresponding acid−base pairs. The experimentally determined cation structures are compared with structures computed by DFT methods. Detailed experimental procedures are given.