Revisiting the Effects of the Molecular Structure in the Kinetics of Electron transfer of Quinones: Kinetic Differences in Structural Isomers
Carlos Frontana1* and Ignacio González2
1 Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional Departamento de Química, Av. Instituto Politécnico Nacional No. 2508. Col. San Pedro Zacatenco, C. P. 07360. México, DF., México, Tel. 52–55–50613800 Ext. 4001, Fax. 52–55–50613389. *Responsible author: ultrabuho@yahoo.com.mx
2 UAM–Iztapalapa, Depto. de Química, Área de Electroquímica, Apartado postal 55–534, 09340, México, D.F.
Recibido el 11 de octubre del 2007 ]]> Aceptado el 16 de diciembre de 2007
Abstract
The effect of 2,5 and 2,6 disubstitution (R = CH3, Cl, C(CH3)3) for 1,4–benzoquinones, in the reorganization energy (λ) for the first electron uptake process was analyzed in acetonitrile solution. Data obtained by cyclic voltammetry suggested differences in λ for each type of disubstitution analyzed. These differences have important consequences in the stability and structure of the electro–generated benzosemiquinone species, which was verified by performing in–situ spectroelectrochemical–ESR (Electron Spin Resonance) experiments of each disubstituted semiquinone.
Key words: Quinone, substituent effect, cyclic voltammetry, inner reorganization energy, ESR.
Resumen
El efecto de la disustitución 2,5 y 2,6 (R = CH3, Cl, C(CH3)3) para diferentes 1,4–benzoquinonas, en la energía de reorganización (λ) para el primer proceso de reducción analizado en acetonitrilo. Los datos obtenidos por voltamperometría cíclica sugieren diferencias en λ entre cada tipo de disustitución analizada. Estas diferencias tienen consecuencias importantes en la estabilidad y estructura de las especies benzo–semiquinona electrogeneradas, lo que fue evidenciado en el análisis in situ espectroelectroquímico–ESR (Resonancia del Espín Electrónico) de cada semiquinona disustituida.
Palabras clave: Quinona, efecto de sustituyente, voltamperometría cíclica, energía de reorganización interna, ESR.
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Acknowledgments
The authors thank Dr. Alejandro Solano–Peralta, (Facultad de Química, UNAM), for his help in the ESR spectra acquisition. C. Frontana thanks CONACyT and SNI–Mexico for the grants and funding given for his Ph. D. and postdoctoral studies.
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