Theoretical NMR Spectroscopic Analysis of the Intramolecular Proton Transfer Mechanism in o r t h o -Hydroxyaryl (Un-)Substitued Schiff Bases

• Autores: Zarycz, Maria Natalia Cristina; Aucar, Gustavo Adolfo
• Año de publicación: 2008
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: BASIS SETS; CHEMICAL CALCULATIONS; MOLECULAR STRUCTURE; NITROGEN; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

Both NMR spectroscopic parameters are calculated as a function of the distance d(N−H) of the O···H···N subsystem of (un- or Z-) substituted ortho-hydroxyaryl Schiff bases, with Z = 4-OMe and 5-Cl. Typical patterns for NMR J couplings and magnetic shieldings, σ(N) (or the chemical shift δ(N)), are obtained showing that they are reliable sensors from which one can get a deeper insight on the intramolecular proton transfer mechanism. An inflection point is found by representing each NMR spectroscopic parameter as a function of d(N−H) or when the correlation between both parameters is depicted. The analysis of these (cubic) functions shows whether the proton is bound to the oxygen or to the nitrogen atom or is shared by both atoms. In line with these findings, it is possible to predict the position of the proton in the bridge. These theoretical findings are supported by previous experimental measurements. It is shown that nitrogen chemical shift is quite sensitive to substituent effects though 1J(15NH) is not. This last parameter depends on d(NH). When correlating both spectroscopic parameters, a previous δ(N) vs 1J(15NH) linear dependence is generalized to a cubic dependence which seems to be more reliable. Calculations are based on two state of the art methodologies: DFT-B3LYP and polarization propagators at second order of approach (SOPPA) with large enough basis sets.
Fil: Zarycz, Maria Natalia Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Física; Argentina
Fil: Aucar, Gustavo Adolfo. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentina