Covalence and π-electron delocalization influence on hydrogen bonds in proton transfer process of <i>o</i>-hydroxy aryl Schiff bases: A combined NMR and QTAIM analysis

Within the framework of density functional theory approach, we studied relationship between chemical nature intramolecular hydrogen bonds (HBs) and nuclear magnetic resonance (NMR) parameters, J-couplings 1H-chemical shifts [δ(1H)], atoms involved in such o-hydroxyaryl Schiff bases during proton transfer process. For first time, shape dependence degree covalence HBs on 1J(N–H), 1J(O–H), 2hJ(O–N), δ(1H) process was analyzed. Parameters obtained from Bader’s molecules were used to assess covalent character with both NMR properties. The influence π-electronic delocalization 2hJ(N–O) under investigated. 2hJ(O–N) a Mannich base also order compare results an unsaturated system. In addition, substituent effects phenolic ring Our indicate that sides transition state undergoes smooth exponential increase as moves downfield. N⋯H (O⋯H) bond increases linearly 1J(N–H) (1J(O–H)) becomes more negative, even after reaching state. Non-vanishing values spin dipolar (SD) paramagnetic orbital terms show has non-negligible effect tautomeric equilibrium gives evidence presence assisted HB.Variation SD term follows similar pattern change para-delocalization aromaticity index chelate ring.