DFT-Aided Vibrational Circular Dichroism Spectroscopy Study of (-)-S-cotinine
Pilar G Rodríguez Ortega1, Manuel Montejo2, Fernando Márquez1
1Department of Physical and Analytical Chemistry, University of Jaén, 23071 Jaén (Spain).
Summary
Vibrational circular dichroism spectroscopy and DFT calculations reveal the conformational distribution of (-)-S-cotinine in solution. Hyperconjugation, not solvent polarity, governs its conformational equilibrium.
Area of Science:
- Chemical Physics
- Spectroscopy
- Computational Chemistry
Background:
- Understanding molecular conformation is crucial in chemistry and pharmacology.
- Chiral molecules present unique conformational challenges due to their non-superimposable mirror images.
Purpose of the Study:
- To determine the solution-state conformational distribution of (-)-S-cotinine.
- To demonstrate the conformer-discriminating power of vibrational circular dichroism (VCD) spectroscopy.
- To elucidate the electronic factors governing the conformational equilibrium.
Main Methods:
- Vibrational circular dichroism (VCD) spectroscopy was employed to analyze (-)-S-cotinine in solution.
- Density Functional Theory (DFT) calculations were performed to interpret the VCD spectra.
- Natural Bond Orbital (NBO) analysis was used to investigate electronic structure and rotational barriers.
Main Results:
- The study successfully determined the conformational distribution of (-)-S-cotinine in solution.
- VCD spectroscopy proved effective in distinguishing between subtly different molecular conformers of chiral samples.
- DFT and NBO calculations identified hyperconjugative effects as the primary driver of the conformational equilibrium.
- Solvent polarity had a negligible impact on the conformational landscape.
Conclusions:
- The combined VCD and DFT approach offers a powerful method for conformational analysis of chiral molecules.
- Hyperconjugation plays a significant role in dictating the conformational preferences of (-)-S-cotinine.
- The conformational behavior of (-)-S-cotinine is largely independent of solvent polarity.
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