Use of Charge‐Charge Repulsion to Enhance π‐Electron Delocalization into Anti‐Aromatic and Aromatic Systems

• Published in: Chemistry : a European journal Vol. 23; no. 11; pp. 2566 - 2570
• Main Authors: Sumita, Akinari, Gasonoo, Makafui, Boblak, Kenneth J., Ohwada, Tomohiko, Klumpp, Douglas A
• Format: Journal Article
• Language: English
• Published: Germany 21-02-2017
• Subjects: anti-aromatic; aromatic; Cations; Diamagnetism; dication; Electrostatics; Mathematical analysis; NMR spectroscopy; Nuclear magnetic resonance; Ring currents; superacid; trication; aromatic; anti-aromatic; superacid; trication; dication
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201606036

A series of 9‐fluorenyl cations has been studied and it is shown that increasing charge on a heterocyclic substituent group enhances the anti‐aromatic character of the carbocation system. Similarly, a series of dibenzosuberenyl cations has been studied and increasing charge on a substituent group is shown to enhance aromatic character in the carbocation system. These studies include the direct observations of dicationic and tricationic species using stable‐ion conditions and low temperature NMR. The structures of these ions were further characterized using DFT calculations, confirming that highly charged organic ions may exhibit unusual distributions of π‐electrons and delocalization of electrons in 4n or 4n+2 π‐systems.
A take‐charge attitude! Electron delocalization is studied within conjugated ring systems using NMR spectroscopy and DFT calculations. Variation of the choice of substituent reveals that paramagnetic (anti‐aromatic) and diamagnetic (aromatic) ring currents can be influenced through electrostatic effects.