Constrained Clar formulas of coronoid hydrocarbons
Jun-ichi Aihara1, Masakazu Makino
1Department of Chemistry, Faculty of Science, Shizuoka University , Oya, Shizuoka 422-8529, Japan.
The Journal of Physical Chemistry. A
|February 11, 2014
Summary
The aromaticity of coronoid hydrocarbons depends on their shape. Macrocyclic conjugation and stabilization energy are influenced by the arrangement of aromatic sextets, especially with central cavities.
Area of Science:
- Organic Chemistry
- Computational Chemistry
- Materials Science
Background:
- Coronoid hydrocarbons exhibit complex aromatic character.
- The interplay between molecular structure and aromaticity is crucial for understanding their properties.
Purpose of the Study:
- To investigate the influence of coronoid hydrocarbon structure on their aromatic character.
- To analyze the impact of macrocyclic conjugation and central cavities on aromatic stabilization energy.
Main Methods:
- Analysis of Clar formulas for various coronoid structures.
- Calculation of aromatic stabilization energy due to macrocyclic conjugation [SSE(mc)].
- Assessment of Nuclear Independent Chemical Shift (NICS(1)) values at the central cavity.
Main Results:
- Aromaticity is primarily determined by the shape of outer and inner peripheries, with jutting benzene rings on armchair edges being most aromatic.
- The presence of a central cavity can restrict the placement of aromatic sextets, affecting overall aromaticity.
- Macrocyclic conjugation [SSE(mc)] and NICS(1) values are strongly dependent on the superposed Clar formula structure.
- Localization of π-electrons in fixed aromatic sextets inhibits macrocyclic conjugation.
- The sign of SSE(mc) is dictated by the number of carbon atoms in the hub cycle.
Conclusions:
- Coronoid hydrocarbon aromaticity is a nuanced property influenced by peripheral structure and internal cavity effects.
- The arrangement of aromatic sextets and the extent of macrocyclic conjugation are key determinants of stabilization energy and magnetic shielding.
- Understanding these structure-aromaticity relationships is vital for designing novel polycyclic aromatic hydrocarbons with tailored electronic properties.
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