781-36-2Relevant academic research and scientific papers
Electrochemical oxidation and EPR spectroscopy of radical cations of N-substituted 2,3,4,5-Tetramethylpyrroles
Klu?k, Robert,Kubá?ek, Pavel
, p. 399 - 406 (2007/10/03)
Electrochemical oxidation of 19 N-substituted 2,3,4,5-tetramethylpyrroles has been studied in acetonitrile and dichloromethane by means of slow cyclic voltammetry and coulometry. The first oxidation consumes one electron and occurs within the potential range 0.60-0.94 V in acetonitrile and 0.78-1.17 V in dichloromethane (vs. SCE). Twelve in situ generated primary radical cations were sufficiently stable at lowered temperature in dichloromethane for EPR measurement and showed well resolved HFS. The g-values (≈2.0026) and the coupling constants of 2,5-methyls (aH≈1.5 mT), 3,4-methyls (aH≈0.35 mT), and of the pyrrole nitrogen (aN≈0.42 mT) are very proximate for all 12 radical cations. It can be concluded, with support from quantum chemical calculations, that the odd electron is localised entirely on the pyrrole ring in the a2 HOMO of the parent molecule. Despite the odd electron distribution, the stability of the radical cations depends on the particular substituent attached to the pyrrole nitrogen. Acta Chemica Scandinavica 1998.
