Structures and strain energies of small [n]metacyclophanes

The structures and strain energies of various derivatives of [5]- and [6]me tacyclophanes have been computed by employing the density functional method (ADF). They showed a good agreement with the few available X-ray crystal s tructures. The structure of 9,12-dichloro[6]metacyclophane was experimental ly determined at 200/233 K. Contrary to intuition, the incorporation of sp( 2)-hybridised carbon atoms in the oligomethylene chain was found to have a minor influence only on the structure and strain energy of these compounds. It is concluded that small metacyclophanes with potentially interesting in teractions between unsaturated fragments in the bridge and the aromatic rin g or between two aromatic rings, e.g. the so far elusive [1.1]metacyclophan e, are realistic synthetic targets.