An experimental and theoretical study of 1J(13C-14N) coupling constants in nitro-aromatic and nitro-heteroaromatic compounds
Data for 12 nitro derivatives (benzenes, pyrroles, furazans and pyrazoles) are reported, of which some furazans and the three pyrazoles are new. These couplings, in the 9–18 Hz range, were compared with B3LYP/6-311++G(d,p) calculations. Although the agreement is not very good, several interesting consequences can be drawn: the value of the coupling constant is not related to the position in the ring nor to the torsion angle but the dimensionless parameter η. For large η (slow quadrupole relaxation) the triplets are observed while for small η (rapid quadrupole relaxation) a broad triplet or even a broad singlet is observed.