Aromaticity of ring carbo-mers of [N]annulenes and [N]cycloalkanes.
Maps of current density induced by a perpendicular external magnetic field are calculated at the ipsocentric CTOCD-DZ/6-31G**//B3PW91/6-31G** level for ring carbo-mers of [N]-annulenes (closed-shell singlet states of C(3N)H, N = 3 to 7, with q = -1, 0, +1, 0, -1, respectively, and also the triplet ground state for N = 4) and of [N]-cycloalkanes (C(3N)H(qN), N = 3, 4, 5). Strong four-electron diatropic ring currents indicate conventional pi aromaticity for all the singlet and triplet carbo-[N]annulenes studied, with the exception of C(12)H(4), where instead the strong two-electron paratropic ring current is the signature of pi antiaromaticity. The carbo-[N]cycloalkanes (also known as [N]pericyclynes) show only localized pi currents, consistent with non-aromaticity. There is no indication of a 'homo-aromatic' ring current attributable to the in-plane pi orbitals of the inserted C2 units in any of the maps. Consequences for the interpretation of ELF (electron localisation function) populations are discussed.
Soncini
Alessandro
A
Laboratory of Quantum Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, B-3001, Heverlee-Leuven, Belgium.
Fowler
Patrick W
PW
Lepetit
Christine
C
Chauvin
Remi
R
D004583:Electrons; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006844:Hydrocarbons, Cyclic / Q000737:chemistry*; D008280:Magnetics; D008956:Models, Chemical; D011789:Quantum Theory
D006571:Heterocyclic Compounds; D006844:Hydrocarbons, Cyclic