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Conformational Dynamics of o-Fluoro-Substituted Z-Azobenzene.
S K Rastogi1, R A Rogers1, J Shi1
1Department of Chemistry and Biochemistry, Texas State University , San Marcos, Texas 78666, United States.
The Journal of Organic Chemistry
|October 28, 2015
Summary
A conformational analysis of o-fluoro Z-azobenzene shows a slight preference for C-F/π interactions. This study determined the phenyl rotation barrier using NMR and DFT, finding it to be 8-10 kcal/mol.
Area of Science:
- Computational Chemistry
- Organic Chemistry
- Spectroscopy
Background:
- Azobenzene derivatives are important in various chemical applications.
- Understanding molecular conformations and rotational barriers is crucial for predicting chemical behavior.
Purpose of the Study:
- To investigate the conformational preferences of ortho-fluoro Z-azobenzene.
- To determine the rotational barrier of phenyl groups in fluorinated Z-azobenzene using experimental and computational methods.
Main Methods:
- Density Functional Theory (DFT) for conformational analysis and energy calculations.
- X-ray crystallography to corroborate ground-state conformations.
- 2D J-resolved Nuclear Magnetic Resonance (NMR) spectroscopy to study through-space coupling and determine rotational barriers.
Main Results:
- A slight preference for C-F/π interactions in o-fluoro Z-azobenzene was identified (0.3-0.5 kcal/mol).
- Through-space (19)F-(19)F coupling was observed and characterized.
- An experimental phenyl rotation barrier of 8-10 kcal/mol was determined, qualitatively supported by DFT calculations.
Conclusions:
- Ortho-fluorine substitution influences Z-azobenzene conformation through weak C-F/π interactions.
- NMR and DFT methods provide reliable insights into rotational barriers in such systems.
- The determined rotational barrier is consistent with values found in similar hydrocarbon systems.
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