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Acidity Determination by Spectroscopic and Modeling Methods in Monohydroxy- and Dihydroxy-Substituted Coumarins
George R Du Laney1, Caleb Gatlin1, Isaac Jonker1
1Department of Chemistry and Biochemistry, Calvin University, Grand Rapids, Michigan49546-4403, United States.
The Journal of Physical Chemistry. A
|July 16, 2026
Summary
This study determined pKa values for hydroxycoumarins using spectroscopy and computation, revealing new acidity data for six compounds. Structure-acidity relationships were clarified for these important chemical entities.
Area of Science:
- Organic Chemistry
- Physical Chemistry
- Computational Chemistry
Background:
- Hydroxycoumarins are a significant class of compounds with diverse applications.
- Understanding their acidity (pKa) is crucial for predicting chemical behavior and designing new molecules.
- Previous studies have not fully characterized the acidity of all simple hydroxycoumarin derivatives.
Purpose of the Study:
- To determine the pKa values for 15 mono- and disubstituted hydroxycoumarins.
- To investigate the influence of hydroxyl and methyl substituents on hydroxycoumarin acidity.
- To validate computational methods for predicting pKa values in this chemical series.
Main Methods:
- UV-vis absorbance spectroscopy was employed for experimental pKa determination.
- Density Functional Theory (DFT) calculations, including Time-Dependent DFT (TD-DFT), were used to model spectra and predict pKa values.
- A thermodynamic-cycle approach combining gas-phase and solvation free energies was utilized for pKa predictions.
Main Results:
- Experimental pKa values were successfully determined for 15 hydroxycoumarin derivatives.
- Six novel pKa values, including that of 5-hydroxycoumarin, were reported for the first time.
- Computational methods showed strong agreement with experimental UV-vis spectra and accurately predicted pKa values (MAE = 0.65).
Conclusions:
- The study provides a comprehensive dataset of pKa values for simple hydroxycoumarins.
- Both experimental and computational approaches offer valuable insights into structure-acidity relationships.
- The validated computational methods can be applied to predict the acidity of related compounds.
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