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Published on: January 9, 2014
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Vibrational Stark fields in carboxylic acid dimers
Manjusha Boda1, G Naresh Patwari1
1Department of Chemistry, Indian Institute of Technology Bombay, Powai Mumbai 400076, India. naresh@chem.iitb.ac.in.
Physical Chemistry Chemical Physics : PCCP
|February 23, 2022
Summary
Carboxylic acid dimers exhibit stable structures, with substitution influencing electric fields and Stark tuning rates. This study models proton transfer and estimates fluoroformic acid's pKa.
Area of Science:
- Physical chemistry
- Computational chemistry
- Spectroscopy
Background:
- Carboxylic acid dimers are model systems for proton transfer.
- Their stabilization energies show weak dependence on substitution.
- However, electric fields on OH groups are sensitive to substituent effects.
Purpose of the Study:
- To investigate the influence of substitution on electric fields and Stark tuning rates in carboxylic acid dimers.
- To model proton and double proton transfer processes.
- To estimate the pKa of fluoroformic acid.
Main Methods:
- Ab initio calculations using MP2/aug-cc-pVDZ and B3LYP/aug-cc-pVDZ levels.
- Calculation of Stark tuning rates for O-H and O-D stretching vibrations.
- Analysis of electric field effects and linear correlation with pKa.
Main Results:
- Electric field experienced by OH groups depends on the dimer partner's substituents (higher with electron-donating, lower with electron-withdrawing).
- Stark tuning rates (Δν) are weakly dependent on substitution on the carboxylic acid itself.
- Anharmonic O-D frequency shifts are significantly higher than harmonic shifts, indicating strong anharmonicity.
Conclusions:
- Substitution on dimer partners significantly impacts electric fields and Stark tuning rates.
- The study provides insights into proton transfer mechanisms and anharmonicity in carboxylic acid dimers.
- The pKa of fluoroformic acid was estimated to be approximately 0.9 based on observed correlations.
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