NMR J(C,C) scalar coupling analysis of the effects of substituents on the keto-enol tautomeric equilibrium in 2-OH-n-X-pyridines. An experimental and DFT study
In order to study the effect of substituents on the preferential keto/enol forms of six mono-substituted 2-OH-pyridines, the energies corresponding to their DFT-optimized structures for both tautomeric forms were compared. To obtain an idea of how solvent dielectric effects affect such a tautomeric...
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| Autores principales: | , , , |
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| Formato: | JOUR |
| Materias: | |
| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_00268976_v102_n23-24_p2607_DeKowalewski |
| Aporte de: |
| Sumario: | In order to study the effect of substituents on the preferential keto/enol forms of six mono-substituted 2-OH-pyridines, the energies corresponding to their DFT-optimized structures for both tautomeric forms were compared. To obtain an idea of how solvent dielectric effects affect such a tautomeric equilibrium, geometry optimizations were performed considering both an isolated molecule and an infinitely diluted dimethylsulfoxide solution (ε = 46.7). It was found that, for all these compounds, the dielectric solvent effect tends to increase the presence of the keto form. NMR 1J( 13C,13C) and 3J(13C,13C) isotropic couplings were measured for the same mono-substituted 2-OH-pyridines as well as for the corresponding mono-substituted pyridines. These isotropic coupling constants were also calculated within the DFT framework, where all four isotropic contributions, Fermi contact, spin dipolar, paramagnetic spin-orbit and diamagnetic spin-orbit, were taken into account. For the mono-substituted-2-OH-pyridines studied in this work, coupling constants were calculated using both the optimized keto and enol forms. The possible use of these couplings as probes to detect the keto and enol forms is discussed. |
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