Varying electronegativity: Effect of the nature and strength of H-bonding in anilide/aniline/anilinium complexes on the electronegativity of NH-/NH2/NH3+ groups

Application of the Domenicano et al. [A.R. Campanelli, A. Domenicano, F. Ramondo, I. Hargittai, J. Phys. Chem. A, 108 (2004) 4940.] method of estimating group electronegativity from angular geometry of the ring in monosubstituted benzene derivatives allowed us to find out how electronegativity of the NH-/NH2/NH3+ groups in H-bonded complexes of the anilide anion, aniline and the anilinium cation depends on the nature and strength of the H-bond. For complexes in which the NH2 group is only a proton donating moiety the estimated electronegativity of the group increases with an increase of the N…base interatomic distance. An opposite relationship is found for cases where nitrogen is a proton acceptor. The observed relationship between the electronegativity, χ, and the C–N bond lengths as well as the intermolecular N…B (base) or HB (H–base) distances are monotonic when calculated for isolated systems using molecular modeling, for crystal structures (the retrieved data from CSD [F.H. Allen, Acta Crystallogr., Sec. B: Struct. Sci., 58 (2002) 380.]), however, are blurred by numerous crystal packing forces. The modeling was carried out using B3LYP/6-311 + G∗∗ level of theory.