Through‐space 19F–19F spin–spin coupling in ortho‐fluoro Z‐azobenzene

We report through‐space (TS) ¹⁹F–¹⁹F coupling for ortho‐fluoro‐substituted Z ‐azobenzenes. The magnitude of the TS‐coupling constant (^TSJ_FF) ranged from 2.2–5.9 Hz. Using empirical formulas reported in the literature, these coupling constants correspond to non‐bonded F–F distances (d_FF) of 3.0–3.5 Å. These non‐bonded distances are significantly smaller than those determined by X‐ray crystallography or density functional theory, which argues that simple models of ¹⁹F–¹⁹F TS spin–spin coupling solely based d_FF are not applicable. ¹H, ¹³C and ¹⁹F data are reported for both the E and Z isomers of ten fluorinated azobenzenes. Density functional theory [B3YLP/6‐311++G(d,p)] was used to calculate ¹⁹F chemical shifts, and the calculated values deviated 0.3–10.0 ppm compared with experimental values. Copyright © 2015 John Wiley & Sons, Ltd.     

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Supported in part by NSA grant MDA904-89-H-2038, PSC-CUNY grant 662330, and the Center for Discrete Mathematics and Theoretical Computer Science (DIMACS), a National Science Foundation Science and Technology Center under NSF grant STC88-09648.