DIHEDRAL ANGLE AND BOND ANGLE DEPENDENCE OF VICINAL PROTON-FLUORINE SPIN-SPIN COUPLING

From an analysis of the nmr spectra of compounds of fixed and known stereochemistry the vicinal proton-fluorine coupling constant has been found to be a function of dihedral angle; the dependence is like vicinal JHH–a maximum at 0° (ca. 31 Hz), a minimum at 90° (ca. 0 Hz), and a maximum at 180° (ca. 44 Hz)–and not a linear dependence as has been reported. JHF.vic is extremely dependent on bond angle, being ca. 31 Hz for a bond angle near 109° and dropping to 0.9 Hz for a bond angle near 118° (dihedral angle fixed at 0°). Evidence is presented for a bond length dependence of JHF.vic. © 1968, American Chemical Society. All rights reserved.