title: Experimental and theoretical electron density study of a highly twisted polycyclic aromatic hydrocarbon: 4-methyl-[4]helicene.
abstract: Helicenes are molecules of considerable interest in view of their aromaticity which persists despite a marked departure from planarity and because of the extreme potency of some of their metabolites as tumor and mutation promoters. In this study, the electron density of 4-methyl-[4]helicene (or 4-methylbenzo[c]phenanthrene) is studied topologically with an emphasis on the fjord region since this region is where metabolic activation is initiated. The molecule consists of four fused aromatic rings that assume a twisted geometry. This geometry brings two hydrogen atoms into close proximity in the fjord region of the molecule accompanied by the appearance of an intramolecular C-Hdelta+...delta+H-C bond path (an interaction termed hydrogen-hydrogen or H- H bonding to distinguish it from dihydrogen bonding from which it is qualitatively distinct). In addition to the intramolecular H-H interaction, a number of intermolecular interactions are shown to be involved in the packing of this molecule in the crystalline state. The effect of the nonplanarity of the molecule on the local aromaticity of each ring is also discussed.
authors: Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada.
authors: David J
authors: DJ
authors: Wolstenholme
authors: Chérif F
authors: CF
authors: Matta
authors: T Stanley
authors: TS
authors: Cameron
mesh_terms: D018360:Crystallography, X-Ray; D004583:Electrons; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*
chemical_list: C523714:4-methyl-(4)helicene; D011084:Polycyclic Aromatic Hydrocarbons