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Anales de la Asociación Química Argentina
Print version ISSN 0365-0375
Abstract
DANIL DE NAMOR, A. F.; AGUILAR CORNEJO, A. F.; CHAHINE, S. and NOLAN, K.. Solvent effect on the 1H NMR spectra of a pyridinocalix(4)arene derivative and its protonation constants in methanol. An. Asoc. Quím. Argent. [online]. 2004, vol.92, n.1-3, pp.155-164. ISSN 0365-0375.
The solvent effect on the 1H NMR spectra of 5, 11, 17, 23 tetra-tert-butyl-25, 26, 27, 28-tetra-[2-(4-pyridyl) methoxy]calix(4) arene, 1c in a wide range of solvents with different dielectric constants was investigated and the results are discussed. It is shown that the 1H NMR spectrum of this macrocycle is sensitive to the nature of the solvent. In all solvents the ligand shows a distorted ‘cone’ conformation..The aromatic protons show the most significant deshielding effect in acetonitrile, nitromethane and pyridine relative to chlroform, which may be attributed to the interaction of these solvents (acetonitrile,nitromethane) through their methyl groups with the hydrophobic cavity of the ligand. For pyridine, π-π interactions between the pyridyl groups and this solvent may occur. The protonation constants of this ligand in methanol were derived from potentiometric titration data in this solvent. The results are compared with those for structural isomers of 1c as well as with those previously reported for lower rim calix(4)arene derivatives containing aliphatic and alicyclic amines as pendant arms. Protonation constant data show that the affinity of the latter to interact with the proton is greater than that of the former macrocycle in methanol. Final conclusions are given.