On the lack of ring-current aromaticity of (heteroatom) [N]radialenes and their dianions.
Current-density maps, calculated at the ab initio RHF//6-31G**/CTOCD-DZ level, show no significant pi ring current in planar equilateral geometries of neutral and dianionic [N]radialenes, oxocarbons and thiocarbons C(N)Y(N) (q-) (Y=CH(2), O, S; N=4, 5, 6; q=0 (1 a-12 a), 2 (1 b-12 b)). Only the N=3 deltate dianions C(3)Y(3) (2-) (Y=CH(2), O, S (1 b, 5 b and 9 b)) have discernible pi ring current, and then with at most 20-25 % of the strength of the standard benzene current. On the magnetic criterion, lack of current is definitive evidence against aromaticity. Pictorial molecular-orbital analysis within the ipsocentric approach shows this to be an inevitable consequence of the nodal structure of the pi and pi* orbitals of [N]radialene-like systems. On grounds of angular-momentum symmetry, spatial distribution, or both, the HOMO-LUMO excitation does not contribute a significant central diamagnetic ring current.
Domene
Carmen
C
Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK.
Fowler
Patrick W
PW
Jenneskens
Leonardus W
LW
Steiner
Erich
E
D000838:Anions / Q000737:chemistry; D019295:Computational Biology; D008956:Models, Chemical; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*
D000838:Anions; D009930:Organic Chemicals