Assessing Aromaticity in Ions: Evaluating Induced Ring Current and UV-Vis Spectrum-Based Criteria
Junhong Liu1, Xinghan Yang1, Xi Chen1
1Key Laboratory of Catalysis and Energy Materials Chemistry of Ministry of Education & Hubei Key Laboratory of Catalysis and Materials Science, South-Central Minzu University, Wuhan 430074, China.
The Journal of Physical Chemistry. A
|June 4, 2025
Summary
Assessing ion aromaticity requires multiple methods. While magnetic and UV-Vis criteria align, stability metrics like isomerization stabilization energy (ISE) are crucial for a complete understanding of aromaticity in ions.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Quantum Chemistry
Background:
- Aromaticity of ions is a growing research area.
- Magnetic (NMR chemical shifts) and spectrum-based (UV-Vis) criteria are common for evaluating ion aromaticity.
- The reliability of magnetic criteria is debated, while UV-Vis validity is less explored.
Purpose of the Study:
- To reassess the aromaticity of 18 ions using multiple computational methods.
- To compare magnetic and spectrum-based criteria with stability metrics.
- To determine the comprehensive validity of different aromaticity assessment methods for ions.
Main Methods:
- Calculated harmonic oscillator model of aromaticity (HOMA) index.
- Employed gauge-including magnetically induced current (GIMIC) calculations.
- Utilized multicenter index (MCI) and isomerization stabilization energy (ISE) calculations.
Main Results:
- GIMIC predictions consistently matched UV-Vis spectra and NMR chemical shifts for ion aromaticity.
- ISE calculations revealed four ions classified as magnetically (anti)aromatic lacked significant energetic stabilization from cyclic conjugation.
- These four ions exhibited similar π-electron delocalization and bond equalization to other aromatic ions.
Conclusions:
- Spectrum-based and magnetic criteria for ion aromaticity show good agreement.
- Stability-based metrics, particularly ISE, are essential for a comprehensive assessment of aromaticity.
- Complementary use of stability metrics prevents misclassification of ion aromaticity.
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