Long-range spin–spin coupling in N-methyl 2-carbomethoxy-4,6-dinitroaniline
Long-range coupling [Formula: see text] between the amino proton and the C-5 ring proton of N-methyl 2-carbomethoxy-4,6-dinitroaniline (1) was established unequivocally by comparison of the proton magnetic resonance spectra of the 3-d and 5-d analogs of 1 together with the N-deutero derivatives of the above compounds. Deuterium decoupling experiments indicated that meta-deuterium coupling was of the order of band resolution (< 0.2 Hz). Elucidation of the source of long-range coupling with the amino proton enabled the chemical shifts of the aromatic protons to be assigned. The relative magnitude of these chemical shifts is discussed in terms of the shielding effects operative in the predominant conformer in which the amino hydrogen is intramolecularly hydrogen bonded to the oxygen of the ester carbonyl group.