Abstract
Short bridges in (nlmeta- and (nlparacyclophanes with n c 8 bend the benzene ring into a boat shape. Naturally, this influences the properties of the aromatic system, but two seemingly contradictory trends are observed. On the one hand, the chemical reactivity of such small cyclophanes is strongly increased and quite unusual; sometimes, it is remindful of that of a localized cyclohcxatriene-like system. On the other hand, aromatic delocalization appears to be hardly impaired as judged from aromatic carbon-carbon bond lengths and from ring current effccts such as proton chemical shifts and anisotropy of the magnetic susceptibility. In line with recent theoretical analyses implying that dclccalization in benzene is due to the a-system and counteracted by the x-system, it is proposed that bent benzene rings are full-flcdged aromatics, and that their sometimes olcfin-like reactivity is predominantly a consequence of their high strain energy being dramatically rclieved in the initial stages of such reactions.
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