Structure and molecular orbital studies of potentially mutagenic methylchrysenes and their pi-pi* electron...

The mutagenic and carcinogenic potency of 5-methylchrysene contrasts strongly with the lack of such activity in any other monomethylchrysene. In order to improve our understanding of the biochemical properties of these compounds, their electronic and molecular structures and pi-pi* electron donor-acceptor complexes have been examined by X-ray diffraction and molecular orbital methods. The crystal structures of the hydrocarbons chrysene (redetermination), 1-methylchrysene and 6-methylchrysene, and of the 1:1 complexes of 1,3,5-trinitrobenzene with chrysene, 2-methylchrysene, 3-methylchrysene, 4-methylchrysene, 5-methylchrysene, 6-methylchrysene, the 2:1 complex with 1-methylchrysene and the 1:1 complex of 5-methylchrysene with pyromellitic dianhydride have been determined. 5-Methylchrysene, the carcinogenic hydrocarbon, shows considerable disorder alone and in complexes. In the complexes the stacking of molecules involves an alternation of hydrocarbon with complexing agent, with the aromatic ring of 1,3,5-trinitrobenzene lying over a hydrocarbon bond involved in ring fusion, as suggested by a consideration of HOMO's and LUMO's in molecular orbital theory.