On the Lack of Ring-Current Aromaticity of (Heteroatom) [N]Radialenes and their Dianions

✍ Scribed by Carmen Domene; Patrick W. Fowler; Leonardus W. Jenneskens; Erich Steiner

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 290 KB
• Volume: 13
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200600507

✦ Synopsis

Abstract

Current‐density maps, calculated at the ab initio RHF//6–31G**/CTOCD‐DZ level, show no significant π 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 π 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 π and π* 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.