title: Effect of fluorine substitution on the aromaticity of polycyclic hydrocarbons.
abstract: The effect of fluorine substitution on the aromaticity of polycyclic hydrocarbons (PAH) is investigated. Magnetically induced current densities, current pathways, and current strengths, which can be used to assess molecular aromaticity, are calculated using the gauge-including magnetically induced current method (GIMIC). The degree of aromaticity of the individual rings is compared to those obtained using calculated nucleus-independent chemical shifts at the ring centers (NICS(0) and NICS(0)(zz)). Calculations of explicitly integrated current strengths for selected bonds show that the aromatic character of the investigated polycyclic hydrocarbons is weakened upon fluorination. In contrast, the NICS(0) values for the fluorinated benzenes increase noteworthy upon fluorination, predicting a strong strengthening of the aromatic character of the arene rings. The integrated current strengths also yield explicit current pathways for the studied molecules. The current pathways of the investigated linear polyacenes, pyrene, anthanthrene, coronene, ovalene, and phenanthro-ovalene are not significantly affected by  fluorination.  NISC(0) and NICS(0)(zz) calculations provide contradictory degrees of aromaticity of the fused individual ring. Obtained NICS values do not correlate with the current strengths circling around the individual rings.
authors.affiliation: Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtanens plats 1), FIN-00014 Helsinki, Finland. Mikko.Kaipio@helsinki.fi
authors.forename: Mikko
authors.initials: M
authors.lastname: Kaipio
authors.forename: Michael
authors.initials: M
authors.lastname: Patzschke
authors.forename: Heike
authors.initials: H
authors.lastname: Fliegl
authors.forename: Fabio
authors.initials: F
authors.lastname: Pichierri
authors.forename: Dage
authors.initials: D
authors.lastname: Sundholm
mesh_terms: D001554:Benzene / Q000737:chemistry; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry*; D015394:Molecular Structure; D011083:Polycyclic Compounds / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D006845:Hydrocarbons, Fluorinated; D011083:Polycyclic Compounds; D001554:Benzene