title: Local aromaticity of [n]acenes, [n]phenacenes, and [n]helicenes (n = 1-9).
abstract: The local aromaticity of the six-membered rings in three series of benzenoid compounds, namely, the [n]acenes, [n]phenacenes, and [n]helicenes for n = 1-9, has been assessed by means of three probes of local aromaticity based on structural, magnetic, and electron delocalization properties. For [n]acenes our analysis shows that the more reactive inner rings are more aromatic than the outer rings. For [n]phenacenes, all indicators of aromaticity show that the external rings are the most aromatic. From the external to the central ring, the local aromaticity varies in a damped alternate way. The trends for the [n]helicene series are the same as those found for [n]phenacenes. Despite the departure from planarity in [n]helicenes, only a very slight loss of aromaticity is detected in [n]helicenes as compared to the corresponding [n]phenacenes. Finally, because of magnetic couplings between superimposed six-membered rings in the higher members of the [n]helicenes series, we have demonstrated that the NICS indicator of aromaticity artificially increases the local aromaticity of their most external rings.
authors.affiliation: Institut de Química Computacional and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona, Catalonia, Spain.
authors.forename: Guillem
authors.initials: G
authors.lastname: Portella
authors.forename: Jordi
authors.initials: J
authors.lastname: Poater
authors.forename: Josep M
authors.initials: JM
authors.lastname: Bofill
authors.forename: Pere
authors.initials: P
authors.lastname: Alemany
authors.forename: Miquel
authors.initials: M
authors.lastname: Solà