The Proton Resonance Spectra of Furan and Pyrrole

Interpretation of the fine structure of the NMR spectra of some five-membered "aromatic" heterocyclic ring compounds indicates that spin coupling constants between adjacent protons on the ring and those across the ring are approximately equal. This is in contrast to the situation in six-membered rings where coupling constants between protons ortho to one another are much larger than those in the meta position.Quadrupole effects of the N 14 nucleus in pyrrole broaden the NH signal but do not interfere with the spin coupling of the NH proton with other protons. The surprising result is obtained that the spin couplings of the NH proton with α and β protons in the ring are very nearly equal in magnitude.