CH Stretching Region: Computational Modeling of Vibrational Optical Activity
Jana Hudecová1,2, Václav Profant1, Pavlína Novotná3
1Faculty of Mathematics and Physics, Institute of Physics, Charles University , Ke Karlovu 5, 12116, Prague 2, Czech Republic.
Journal of Chemical Theory and Computation
|November 20, 2015
Summary
Computational methods can now interpret complex CH stretching vibrational spectra in organic molecules. This study reveals that anharmonic corrections and specific computational approaches improve accuracy, aiding vibrational spectroscopy applications.
Area of Science:
- Computational Chemistry
- Spectroscopy
- Organic Chemistry
Background:
- Vibrational spectra in the CH stretching region are crucial for organic compound analysis but challenging to interpret due to experimental and computational complexities.
- Understanding factors influencing CH stretching vibrations is essential for advancing vibrational spectroscopy techniques.
Purpose of the Study:
- To evaluate harmonic and anharmonic computational methods for describing CH stretching vibrations in organic molecules.
- To compare computational results with experimental Raman, Raman optical activity (ROA), infrared absorption (IR), and vibrational circular dichroism (VCD) spectra.
Main Methods:
- Quantum chemical computations were employed, including harmonic and anharmonic approaches.
- Spectra of α-pinene, fenchone, and camphor were measured and computationally modeled.
- The mPW2PLYP double-hybrid functional and limited vibrational configuration interaction (LVCI) were utilized for accurate force fields and spectral simulations.
Main Results:
- Harmonic vibrational approaches surprisingly reproduced spectral patterns and vibrational optical activity (VOA) reasonably well.
- CH stretching vibrations showed higher sensitivity to basis set and solvent variations compared to lower-frequency vibrations.
- Anharmonic corrections were necessary for higher accuracy in frequencies and spectral shapes, with LVCI providing the best simulations.
- The mPW2PLYP functional yielded accurate harmonic and anharmonic force fields.
- Unprecedented agreement was achieved for experimental vibrational frequencies, though spectral shapes were less accurately reproduced.
Conclusions:
- Computational modeling, particularly with anharmonic corrections and specific methods like LVCI, significantly enhances the interpretation of CH stretching vibrational spectra.
- The study demonstrates the potential for ab initio interpretation of these spectra in larger organic molecules, expanding the utility of vibrational spectroscopy.
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