Proton-proton double resonance studies of formamide-¹⁵N and N-methylformamide-¹⁵N

Abstract

The magnitudes and some of the relative signs of the 15N-H and H-H couplings in N-methylformamide-15N and formamide-15N have been determined. The 15N-H couplings through one bond in these amides and in ammonia, ammonium ion and pyridinium ion are apparently dominated by the Fermi contact term, pyrrole being exceptional. Other couplings are quite successfully accounted for by the theory worked out for molecules with exclusively carbon frameworks. Changes in the coupling constants of N-methylformamide with dilution in water can be partly explained by an increase in the C-N bond order by interaction with the water solvent.