BAY-REGION AND FJORD-REGION DISTORTIONS IN DIBENZ[A,J]ANTHRACENE AND TETRABENZO[DE,HI,MN,QR]NAPHTHACENE

The crystal structure of 7,14-dimethyldibenz[a,j]anthracene (DMDBA) ha s been determined, and the crystal structure of tetrabenzo[de,hi,mn,qr ]naphthacene (TBNC) has been redetermined at higher precision than pre viously reported. These molecules are polycyclic aromatic hydrocarbons (PAHs) that have, respectively, two hindered bay regions and two fjor d regions; the former PAH is a known carcinogen. The extensive out-of- plane bending as a result of steric overcrowding in the bay and fjord regions in these PAHs is shown by these studies. For DMDBA, the angle between the 14-methyl group and the outer rings is 32.6 degrees. For T BNC, the angle between the outer rings of the molecule is 31.9 degrees . These structures are compared with those of related structures of 7, 12-dimethylbenz[a]anthracene and dibenzo[g,p]chrysene. It appears that steric overcrowding in such PAHs can cause distortions of up to 33 de grees C. Such steric overcrowding will affect the conformations of bay - and fjord-region diolepoxides, which are the presumed activated meta bolites in the carcinogenic process.