Aromaticity of overcrowded nitroanilines
Irena Majerz1, Teresa Dziembowska
1Faculty of Chemistry, University of Wrocław, 50-383 Wrocław, Poland. majerz@yahoo.com
The Journal of Physical Chemistry. A
|May 25, 2012
Summary
Bulky groups in 2,4,6-trinitroanilines impact aromaticity due to intramolecular hydrogen bonds and steric hindrance. Intermolecular interactions in crystals significantly affect aromaticity, as shown by HOMA index and ΔP parameter analysis.
Area of Science:
- Organic Chemistry
- Computational Chemistry
- Physical Chemistry
Background:
- Aromaticity is a key concept in organic chemistry, influencing molecular stability and reactivity.
- Overcrowded aromatic systems, like substituted nitroanilines, present unique structural and electronic challenges.
- Understanding the interplay of electronic and steric effects is crucial for predicting molecular properties.
Purpose of the Study:
- To investigate the influence of intramolecular hydrogen bonds, electronic effects, and steric hindrance on the aromaticity of 2,4,6-trinitroanilines.
- To compare the aromaticity of these molecules in crystalline form versus their optimized structures.
- To elucidate the role of intermolecular interactions and crystal packing on the electronic properties of overcrowded nitroanilines.
Main Methods:
- Density Functional Theory (DFT) calculations using the B3LYP/6-311++G** level of theory.
- Quantification of aromaticity using the Harmonic Oscillator Model of Aromaticity (HOMA) index.
- Assessment of benzene ring planarity using the ΔP parameter and puckering parameters.
- Analysis of intermolecular interactions using the simplified PCM model.
- Natural Bond Orbital (NBO) analysis to study orbital changes upon dearomatisation.
Main Results:
- Bulky substituents significantly influence intramolecular hydrogen bonds, electronic effects, and steric hindrance in 2,4,6-trinitroanilines.
- Aromaticity, measured by the HOMA index, is demonstrably affected by these factors, with deviations from planarity (ΔP) also observed.
- Comparison of crystal and optimized structures reveals a substantial impact of intermolecular interactions and crystal packing on the aromaticity of these overcrowded molecules.
- NBO analysis provided insights into the electronic redistribution associated with dearomatisation.
Conclusions:
- Intermolecular interactions play a critical role in modulating the aromaticity of overcrowded nitroanilines in the solid state.
- Computational methods, including DFT and NBO analysis, are effective tools for studying the complex interplay of factors affecting aromaticity.
- The findings contribute to a deeper understanding of structure-property relationships in substituted aromatic compounds.
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