ANALYSIS OF LONG-RANGE THROUGH-SPACE COUPLINGS VIA AN INTRAMOLECULAR HYDROGEN-BOND

2-Fluorobenzamide and its N-methyl derivative show spin-spin couplings between the aromatic fluorine and the nitrogen and carbon of the amid e group, which are absent in the corresponding N,N-dimethylamide. The N-methyl compound, in which there is a hydrogen bond between the fluor ine and the amide hydrogen, also shows fluorine couplings to the nucle i of the methyl group, and these are diminished for solutions of the a mide in polar solvents. Such couplings are absent in the N,N-dimethyla mide, which does, however, show fluorine couplings to the proximate me thyl group. Calculations at the INDO level employing the IPPP method g ive reasonable agreement with the magnitudes of the observed 4J(F,N) v alues in the N-methylamide and show that the Fermi contact contributio ns are dominant and that the spin information is transmitted mainly th rough the hydrogen bond.