title: NMR structural study of the prototropic equilibrium in solution of Schiff bases as model compounds.
abstract: An NMR titration method has been used to simultaneously measure the acid dissociation constant (pKa) and the intramolecular NHO prototropic constant ΔKNHO 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 1H-, 13C- and 15N-NMR spectroscopy. The physicochemical parameters of the intramolecular NHO hydrogen bond (pKa, ΔKNHO and ΔΔG°) were obtained from 1H-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 δ-diagram analysis and Perrin model data linearization.
authors.affiliation: Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico. dortegon@ucol.mx.
authors.forename: David
authors.initials: D
authors.lastname: Ortegón-Reyna
authors.affiliation: Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico. cgarciam@cinvestav.mx.
authors.forename: Cesar
authors.initials: C
authors.lastname: Garcías-Morales
authors.affiliation: Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico. ipadillamar@ipn.mx.
authors.forename: Itzia
authors.initials: I
authors.lastname: Padilla-Martínez
authors.affiliation: Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico. efren1003@yahoo.com.mx.
authors.forename: Efren
authors.initials: E
authors.lastname: García-Báez
authors.affiliation: Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico. aariza@cinvestav.mx.
authors.forename: Armando
authors.initials: A
authors.lastname: Aríza-Castolo
authors.affiliation: Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico. peraza@ucol.mx.
authors.forename: Ana
authors.initials: A
authors.lastname: Peraza-Campos
authors.affiliation: Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico. fjmartin@ucol.mx.
authors.forename: Francisco
authors.initials: F
authors.lastname: Martínez-Martínez
mesh_terms: D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D012545:Schiff Bases / Q000138:chemical synthesis / Q000737:chemistry*; D012996:Solutions
chemical_list: D012545:Schiff Bases; D012996:Solutions