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Updated: Mar 31, 2026

Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates
Published on: February 15, 2016
Triplet State Aromaticity: NICS Criterion, Hyperconjugation, and Charge Effects
Hongchao Sun1, Ke An1, Jun Zhu2
1State Key Laboratory of Physical Chemistry of Solid Surfaces, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry and, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, Fujian, P. R. China.
Determining triplet-state aromaticity is crucial. Density functional theory calculations reveal NICS(1)zz is the best nuclear-independent chemical shift index for evaluating triplet-state aromaticity, especially for neutral species.
Area of Science:
- Organic Chemistry
- Computational Chemistry
Background:
- Aromaticity is a fundamental concept in organic chemistry.
- Evaluating aromaticity in triplet states remains challenging.
- Nuclear-independent chemical shift (NICS) indices are commonly used but their efficacy for triplet states is debated.
Purpose of the Study:
- To identify the most reliable NICS index for assessing triplet-state aromaticity.
- To investigate the influence of charge on triplet-state aromaticity.
- To explore the role of hyperconjugation in triplet-state aromaticity.
Main Methods:
- Density functional theory (DFT) calculations were employed.
- Various NICS indices were systematically evaluated.
- Correlations between NICS values and aromaticity were analyzed.
Main Results:
- NICS(1)zz was identified as the optimal NICS index for triplet-state aromaticity.
- Considering only neutral species significantly improved correlations (from 0.840 to 0.938).
- Five-membered rings exhibited reversed aromaticity (aromatic to antiaromatic and vice versa) between singlet and triplet states due to hyperconjugation.
- A moderate correlation (r(2) = 0.708) was found between NICS(1)zz and spin distributions.
Conclusions:
- NICS(1)zz is the preferred index for evaluating triplet-state aromaticity.
- Charge significantly impacts triplet-state aromaticity.
- Hyperconjugation plays a key role in the aromatic behavior of cyclic systems in triplet states.
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