Nuclear Magnetic Resonance Spectroscopy. Conformational Properties of Cyclobutanes. Variation of Vicinal Hydrogen—Fluorine Coupling Constants with Temperature

The observation of substantial temperature variations of the vicinal hydrogen-fluorine coupling constants in a series of cyclobutanes is consistent with the existence of an equilibrium between conformations. The temperature dependencies are discussed in terms of the models developed previously. The magnitude of these couplings as a function of the dihedral angle appears to follow a relationship similar to that described by Karplus for proton-proton couplings.