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Acidity of anilines: calculations vs experiment
Lauri Lipping1, Agnes Kütt, Karl Kaupmees
1Institute of Chemistry, University of Tartu, 14a Ravila St., 50411 Tartu, Estonia. walf@ut.ee
The Journal of Physical Chemistry. A
|August 12, 2011
Summary
Density functional theory accurately predicts gas-phase acidities for substituted anilines. Aniline anion substituent effects significantly influence acidity more than neutral molecule effects.
Area of Science:
- Computational Chemistry
- Physical Organic Chemistry
Background:
- Aniline acidity is crucial for understanding chemical reactivity.
- Quantifying substituent effects on aniline acidity requires accurate theoretical models.
Purpose of the Study:
- To calculate gas-phase acidities of monosubstituted anilines using Density Functional Theory (DFT).
- To analyze substituent effects on both neutral anilines and their conjugate anions.
- To evaluate the performance of the COSMO-RS model for predicting pK(a) in DMSO.
Main Methods:
- Density Functional Theory (DFT) at the B3LYP/6-311+G** level for acidity calculations.
- Isodesmic homodesmotic reactions for dissecting substituent effects.
- COSMO-RS model for pK(a) prediction in DMSO.
Main Results:
- DFT calculations showed good correlation with experimental gas-phase acidities (R²=0.990).
- Substituent effects on the aniline anion were found to be more significant than on the neutral aniline.
- COSMO-RS accurately predicted pK(a) trends in DMSO (R²=0.980) but underestimated absolute values.
Conclusions:
- DFT provides a reliable method for predicting aniline gas-phase acidities.
- Anion stabilization plays a dominant role in the substituent effects on aniline acidity.
- COSMO-RS is a promising tool for predicting pK(a) trends in solution, with potential for refinement.
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