Properties of aromaticity indices based on the one-electron density matrix
Jerzy Cioslowski1, Eduard Matito, Miquel Solà
1Institute of Physics, University of Szczecin, Wielkopolska 15, 70-451 Szczecin, Poland. jerzy@kyoko.chem.fsu.edu
The Journal of Physical Chemistry. A
|June 23, 2007
Summary
Normalized indices accurately measure aromaticity in annulenes and polycyclic systems using Hückel molecular orbital theory. The ING index, when calculated with specific methods, properly orders heterocyclic aromaticity.
Area of Science:
- Quantum Chemistry
- Theoretical Chemistry
- Computational Chemistry
Background:
- Aromaticity is a key concept in chemistry, influencing molecular stability and reactivity.
- Existing methods for quantifying aromaticity can be complex or limited in scope.
Purpose of the Study:
- To develop and validate normalized indices for measuring molecular aromaticity.
- To compare the performance of different indices, particularly the ING index, for various molecular systems.
Main Methods:
- Normalization of existing indices to create new aromaticity measures.
- Computation within the Hückel molecular orbital (HMO) approximation.
- Application of the Giambiagi formula and Atoms in Molecule (AIM) partitioning for the ING index.
- Analysis of electron correlation effects on aromaticity measures.
Main Results:
- Normalized indices closely match topological resonance energies for aromatic annulenes.
- Indices are applicable to both homocyclic and heterocyclic compounds.
- The ING index, under specific conditions (all-electron wavefunctions, AIM partitioning), correctly orders heterocyclic aromaticity.
- Electron correlation significantly impacts ING index values.
Conclusions:
- Normalized indices provide a reliable method for assessing aromaticity in diverse systems.
- The ING index is suitable for aromatic species but may not distinguish anti- and nonaromatic systems.
- Computational level and partitioning method are crucial for accurate aromaticity assessment.
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