Effect of Basic Site Substituents on Concerted Proton–Electron Transfer in Hydrogen-Bonded Pyridyl–Phenols
| Autor: | Antonio G. DiPasquale, Todd F. Markle, James M. Mayer, Werner Kaminsky, Tristan A. Tronic |
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| Rok vydání: | 2012 |
| Předmět: |
Models
Molecular Phenol Proton Pyridines Chemistry Molecular Conformation Hydrogen Bonding Photochemistry Medicinal chemistry Article Electron Transport Electron transfer chemistry.chemical_compound Reaction rate constant Pyridine Proton NMR Phenols Protons Physical and Theoretical Chemistry Methylene Diimine |
| Zdroj: | The Journal of Physical Chemistry A. 116:12249-12259 |
| ISSN: | 1520-5215 1089-5639 |
| DOI: | 10.1021/jp311388n |
| Popis: | Separated concerted proton-electron transfer (sCPET) reactions of two series of phenols with pendent substituted pyridyl moieties are described. The pyridine is either attached directly to the phenol (HOAr-pyX) or connected through a methylene linker (HOArCH(2)pyX) (X = 4-NO(2), 5-CF(3), 4-CH(3), and 4-NMe(2)). Electron-donating and -withdrawing substituents have a substantial effect on the chemical environment of the transferring proton, as indicated by IR and (1)H NMR spectra, X-ray structures, and computational studies. One-electron oxidation of the phenols occurs concomitantly with proton transfer from the phenolic oxygen to the pyridyl nitrogen. The oxidation potentials vary linearly with the pK(a) of the free pyridine (pyX), with slopes slightly below the Nerstian value of 59 mV/pK(a). For the HOArCH(2)pyX series, the rate constants k(sCPET) for oxidation by NAr(3)(•+) or [Fe(diimine)(3)](3+) vary primarily with the thermodynamic driving force (ΔG°(sCPET)), whether ΔG° is changed by varying the potential of the oxidant or the substituent on the pyridine, indicating a constant intrinsic barrier λ. In contrast, the substituents in the HOAr-pyX series affect λ as well as ΔG°(sCPET), and compounds with electron-withdrawing substituents have significantly lower reactivity. The relationship between the structural and spectroscopic properties of the phenols and their CPET reactivity is discussed. |
| Databáze: | OpenAIRE |
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