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Comparative study of aromaticity in tetraoxa[8]circulenes
Slavko Radenković1, Ivan Gutman, Patrick Bultinck
1Faculty of Science, University of Kragujevac, 12 Radoja Domanovića, 34000 Kragujevac, Serbia. slavkoradenkovic@kg.ac.rs
The Journal of Physical Chemistry. A
|September 4, 2012
Summary
The central ring of tetraoxa[8]circulene is antiaromatic, while its fused rings are aromatic. Benzo-annelation enhances aromaticity in five-membered rings and reduces antiaromaticity in eight-membered rings.
Area of Science:
- Computational chemistry
- Organic chemistry
- Aromaticity studies
Background:
- Tetraoxa[8]circulene and its derivatives are macrocyclic compounds with potential electronic applications.
- Understanding local aromaticity is crucial for predicting molecular properties and reactivity.
- Previous studies have explored the aromaticity of similar macrocycles, but detailed analysis of tetraoxa[8]circulene remains limited.
Purpose of the Study:
- To investigate the local aromaticity distribution within tetraoxa[8]circulene and its benzo-annelated derivatives.
- To evaluate the influence of benzo-annelation on the aromatic and antiaromatic character of the rings.
- To establish structure-property relationships based on aromaticity.
Main Methods:
- Utilized a suite of computational aromaticity indices: energy effect (ef), multicenter delocalization indices (MCI), harmonic oscillator model of aromaticity (HOMA), nucleus independent chemical shifts (NICS), and ring current maps.
- Performed detailed analysis of electron delocalization and magnetic field response.
- Calculated current density distribution to visualize aromatic currents.
Main Results:
- The central eight-membered ring of tetraoxa[8]circulene exhibits antiaromatic character, while the furanoid and benzenoid rings are aromatic.
- The "annulene within an annulene" model is not applicable to describe the aromaticity of these systems.
- Benzo-annelation increases aromaticity in the five-membered rings and decreases antiaromaticity in the eight-membered rings, with effects proportional to the number of fused rings.
Conclusions:
- Tetraoxa[8]circulene possesses a complex aromaticity profile with distinct characteristics for its central and peripheral rings.
- Benzo-annelation provides a tunable strategy to modulate the aromaticity and antiaromaticity of these macrocycles.
- The pairwise energy effect (pef) of cyclic conjugation effectively explains the observed trends in aromaticity.
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