NMR Structural Study of the Prototropic Equilibrium in Solution of Schiff Bases as Model Compounds

作者：Ortegon Reyna David; Garcias Morales Cesar; Padilla Martinez Itzia; Garcia Baez Efren; Ariza Castolo Armando; Peraza Campos Ana; Martinez Martinez Francisco^*

来源：Molecules, 2014, 19(1): 459-481.

DOI：10.3390/molecules19010459

• Schiff bases
• NHO prototropic tautomerism
• NMR titration
• delta-diagram

An NMR titration method has been used to simultaneously measure the acid dissociation constant (pK(a)) and the intramolecular NHO prototropic constant Delta K-NHO on a set of Schiff bases. The model compounds were synthesized from benzylamine and substituted ortho-hydroxyaldehydes, appropriately substituted with electron-donating and electron-withdrawing groups to modulate the acidity of the intramolecular NHO hydrogen bond. The structure in solution was established by H-1-, C-13- and N-15-NMR spectroscopy. The physicochemical parameters of the intramolecular NHO hydrogen bond (pK(a), Delta K-NHO and Delta Delta G degrees) were obtained from H-1-NMR titration data and pH measurements. The Henderson-Hasselbalch data analysis indicated that the systems are weakly acidic, and the predominant NHO equilibrium was established using Polster-Lachmann delta-diagram analysis and Perrin model data linearization.

• 出版日期2014-1