Conformational Dynamics of o-Fluoro-Substituted Z-Azobenzene.
A conformational analysis of o-fluoro Z-azobenzene reveals a slight preference for aromatic C-F/π interaction. Density functional theory (DFT) indicates that the conformation with a C-F/π interaction is preferred by approximately 0.3-0.5 kcal/mol. Ground-state conformations were corroborated with X-ray crystallography. (Z)-Azobenzene (Z-AB) with at least one o-fluoro per ring displays (19)F-(19)F through-space (TS) coupling. 2D J-resolved NMR was used to distinguish through-bond from TS coupling ((TS)JFF). (TS)JFF decreases as the temperature is lowered and the multiplets coalesce into broad singlets. We hypothesize that the coalescence temperature (Tc) corresponds to the barrier for phenyl rotation. The experimentally determined barrier of 8-10 kcal/mol has been qualitatively verified by DFT where transition states with a bisected geometry were identified with zero-point energies of 6-9 kcal/mol relative to ground state. These values are significantly higher that values estimated from previous theoretical studies but lie within a reasonable range for phenyl rotation in hydrocarbon systems.
Department of Chemistry and Biochemistry, Texas State University , San Marcos, Texas 78666, United States.
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Rastogi
Department of Chemistry and Biochemistry, Texas State University , San Marcos, Texas 78666, United States.
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Rogers
Department of Chemistry and Biochemistry, Texas State University , San Marcos, Texas 78666, United States.
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Shi
Department of Chemistry, The University of Akron , Akron, Ohio 44325, United States.
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Gao
Department of Chemistry, The University of Akron , Akron, Ohio 44325, United States.
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Rinaldi
Department of Chemistry and Biochemistry, Texas State University , San Marcos, Texas 78666, United States.
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Brittain