SHAPES OF CARCINOGENIC BENZ[A]ANTHRACENES - X-RAY CRYSTAL-STRUCTURE ANALYSIS OF 12-METHYLBENZ[A]ANTHRACENE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 1  (6) , 281-288
Abstract
The crystal structure of the moderately active carcinogen 12-methylbenz[a]anthracene (12-MBA) was determined by application of direct methods to X-ray single crystal diffraction data. Least squares refinement to a residual R = 0.09 over 929 independent reflections enabled C positions to be established with apparent e.s.d.s of atomic coordinates .apprx. 0.008 .ANG.. Deviation from planarity is exemplified by the 15.5.degree. inclination of the benz ring (A) to the anthracene nucleus and the 0.89 .ANG. distance of the methyl C out of the best plane through the whole benzanthracene nucleus. Comparison with the structure of the highly carcinogenic 7,12-dimethylbenz[a]anthracene (7,12-DMBA), and the recently solved structures of the weak carcinogen 1-MBA and the extremely weak carcinogen 1,12-DMBA, shows a close similarity in the anthracene parts. In 1-MBA, 12-MBA and 1,12-DMBA, the phenanthrenic K-region bond is close to 1.34 .ANG. and the M-region bond .apprx. 138 .ANG.. In 12-MBA, overcrowding in the bay region causes the central anthracene ring C and the benz ring A each to be bent about 10.degree. in opposite directions from the phenanthrenic B ring, much as in 1-MBA and 7,12-DMBA, but less than in 1,12-DMBA. The 12-methyl C lies about the same distance (0.55 .ANG.) above the anthracene plane in 12-MBA as in 1,12-MBA and 7,12-DMBA.

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