The Structure of Hexabenzotriphenylene and the Problem of Overcrowded “<i>D</i><sub>3</sub><i><sub>h</sub></i>” Polycyclic Aromatic Compounds

Hexabenzotriphenylene (<b>1</b>, dibenzo[<i>f,j</i>]phenanthro[9,10-<i>s</i>]picene) has been prepared in 5% yield by vacuum pyrolysis of phenanthrene-9,10-dicarboxylic anhydride, and its X-ray structure has been determined. Compound <b>1</b> is a strongly twisted, <i>D</i><sub>3</sub>-symmetric molecular propeller, in contrast to other highly substituted triphenylenes (perfluoro- and perchlorotriphenylene) which adopt <i>C</i><sub>2</sub>-symmetric conformations. Computational studies of these and other overcrowded, nominally <i>D</i><sub>3</sub><i><sub>h</sub></i>-symmetric, polycyclic aromatic compounds are reported, and the origins of their conformational preferences and the adequacy of various computational methods for treating these compounds are discussed.