X-ray crystal structures of a benzonorbornenyl cation and of a protonated benzonorbornenol

摘要

The crystal structure of the 9-methylbenzonorbomenyl cation Me-1(+) shows a relatively strong interaction between the sp(2)-hybridized carbon atom C9 and the aromatic ring (C4a-C9 equivalent to C8a-C9 = 1.897(10) Angstrom). The anion Sb2F11- is refined as rotationally disordered along the (SbSb)-Sb-... axis. In sharp contrast to the findings about Me-1(+), the protonated anti-benzonorbornenol 5(+) 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-1(+). 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 pK(a) 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.