Coupling constants involving fluorine atoms are solvent and temperature dependent: for example, for the derivative ClF a difference of ∼85 Hz has been found for 1J(35Cl, 19F) between the liquid and the gasphase.

What affects coupling constant?

The major factors affecting coupling constants are dihedral angles, substituents, hybridization, and ring strain.

Do coupling constants change?

For a molecule with a single J-coupling constant, the appearance of the NMR spectrum is unchanged if the sign of the coupling constant is reversed, although spectral lines at given positions may represent different transitions.