Sign of JHF in CHFCl2

Abstract

If a nuclear spin is relaxed by two relaxation mechanisms with the same correlation time, the NMR lines may have differing relaxation rates. The fluorine nuclear spin in CHFCl₂ at low temperature is relaxed by dipole—dipole interaction and by an anisotropy in the chemical shift. The sign of the coupling constant between fluorine and hydrogen (J_HF) has been determined from the relaxation pattern. J_HF turns out to be positive.