DIBENZO[A,L]PYRENE (DIBENZO[DEF,P]CHRYSENE) - FJORD-REGION DISTORTIONS

The molecular dimensions of the potent chemical carcinogen dibenzo[def ,p]chrysene, also known as dibenzo[a,l]pyrene, have been determined by X-ray diffraction methods. This analysis shows that the molecule is c onsiderably distorted so that it is non-planar with an angle of 27.6 d egrees between the outermost rings and a widening of C-C-C bond angles in the fjord region. The dimensions of the molecular distortion due t o atomic overcrowding in the fjord region are presented. This polycycl ic aromatic hydrocarbon is a more potent carcinogen than is benzo[a]py rene or its 11-methyl derivative. Comparisons of the distortions in di benzo[a,l]pyrene with the geometries of various other polycyclic aroma tic hydrocarbons containing fjord- or bay-region methyl groups provide structural data on the ratio of angular to torsional distortion in su ch overcrowded molecules.