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Conformational Equilibrium and Internal Dynamics of E-Anethole: A Rotational Study
Camilla Calabrese1, Qian Gou1, Assimo Maris1
1Dipartimento di Chimica "G. Ciamician" dell'Università , Via Selmi 2, I-40126 Bologna, Italy.
The Journal of Physical Chemistry. B
|June 25, 2016
Summary
The rotational spectra of E-anethole's anti and syn conformers were studied. The anti conformer is the global minimum, offering new insights into molecular structure and energy.
Area of Science:
- Molecular Spectroscopy
- Quantum Chemistry
- Computational Chemistry
Background:
- E-anethole exists in anti and syn conformers, differing in the orientation of side chains relative to the benzene ring.
- Previous theoretical studies yielded conflicting results regarding the relative stability of these conformers.
Purpose of the Study:
- To experimentally determine the relative energies of E-anethole conformers.
- To investigate the internal rotation barriers of the propenyl group in both conformers.
- To resolve discrepancies in existing theoretical predictions.
Main Methods:
- Free jet broadband millimeter-wave spectroscopy was employed to record high-resolution rotational spectra.
- Quantum chemical calculations were performed to support experimental data analysis.
- Relative intensity measurements of spectral lines were used for energy difference determination.
Main Results:
- The anti conformer of E-anethole was identified as the global minimum, being approximately 2.0(5) kJ mol(-1) more stable than the syn conformer.
- Low barriers to internal rotation of the propenyl methyl group were determined for both conformers (7.080(5) and 6.978(4) kJ mol(-1)).
- Fully resolved A-E splittings of rotational transitions were observed due to these low barriers.
Conclusions:
- This study experimentally confirms the anti conformer as the most stable form of E-anethole.
- The findings resolve conflicting theoretical predictions regarding E-anethole's conformational preferences.
- Accurate determination of internal rotation barriers provides valuable data for understanding molecular dynamics.
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