Dibenzo[a,l]pyrene (dibenzo[def,p]chrysene): fjord-region distortions

The molecular dimensions of the potent chemical carcinogendibenzo[def,p]chrysene, also known as dibenzo[a,l]pyrene, have beendetermined by X-ray diffraction methods. This analysis shows that themolecule is considerably distorted so that it is non-planar with an angleof 27.6 degrees between the outermost rings and a widening of C-C- C bondangles in the fjord region. The dimensions of the molecular distortion dueto atomic overcrowding in the fjord region are presented. This polycyclicaromatic hydrocarbon is a more potent carcinogen than is benzo[a]pyrene orits 11-methyl derivative. Comparisons of the distortions indibenzo[a,l]pyrene with the geometries of various other polycyclic aromatichydrocarbons containing fjord- or bay-region methyl groups providestructural data on the ratio of angular to torsional distortion in suchovercrowded molecules.