Jones D W, Shaw J D
Carcinogenesis. 1987 Sep;8(9):1323-6. doi: 10.1093/carcin/8.9.1323.
The molecular and crystal structure of 1,12-dimethylbenz[a]anthracene, one of the least carcinogenic of the benz[a]anthracenes, has been refined, from new X-ray diffractometric data collected at room temperature, to an R index 0.047 over 1217 independent reflections. Improved determination of molecular geometry shows that steric strain arising from the presence of two bay-methyl substituents causes even greater molecular distortion than in the highly carcinogenic 7,12-dimethylbenz[a]anthracene, with the benzo A ring inclined at about 29 degrees to the furthest C and D rings. Methyl carbon atoms are displaced 1.0 and 1.3 A on opposite sides of the mean molecular plane and the beach bond of the bay region is 1.480(4) A long, flanked by C-C-C angles of 124.3 and 125.0 degrees. The shortest carbon-carbon bond is C5-C6 = 1.327(5) A at the K region, with the next shortest C8-C9 = 1.346(6) A. Close intramolecular approaches of methyl hydrogens across the bay and to nearest aromatic hydrogens are 2.3-2.6 A.
1,12 - 二甲基苯并[a]蒽是苯并[a]蒽中致癌性最低的物质之一，利用在室温下收集的新的X射线衍射数据对其分子结构和晶体结构进行了精修，在1217个独立反射上的R指数为0.047。对分子几何结构的改进测定表明，两个湾区甲基取代基的存在所产生的空间应变导致的分子畸变甚至比高致癌性的7,12 - 二甲基苯并[a]蒽更大，其中苯并A环与最远的C环和D环倾斜约29度。甲基碳原子在平均分子平面的两侧分别位移了1.0和1.3 Å，湾区的滩键长为1.480(4) Å，两侧的C - C - C角为124.3度和125.0度。最短的碳 - 碳键在K区域，为C5 - C6 = 1.327(5) Å，次短的为C8 - C9 = 1.346(6) Å。甲基氢原子穿过湾区与最近的芳香氢原子的分子内近距离接近距离为2.3 - 2.6 Å。
