title: An EPR analysis of β-dimerization in α-blocked pyrroles in oxidant conditions.
abstract: Electron paramagnetic resonance (EPR) analysis of neutral and acidic solutions of 2,5-dimethyl-1-phenylpyrrol (1) and meta-, para-, and ortho-bis(2,5-dimethylpyrrol-1-yl)benzenes (4-6) in the presence of Tl(III) trifluoroacetate as oxidant reveals the poor stability of their generated monomeric radical cations which dimerize through C(β)-C(β) bond formation. EPR spectra of the monomeric radical cations 4(•+) , 5(•+) , and 6(•+) coincide with that of 1(•+) , suggesting that the unpaired electron in these charged species is confined in one of the pyrrolic rings. The very twisted angles between pyrrolic and phenyl planes due to steric hindrance in the X-ray analysis of the molecular structure of 4 confirm the absence of extended conjugation in the π-system.
authors: Departament de Química Biològica i Modelització Molecular, Institut de Química Avançada de Catalunya (CSIC), Barcelona, Spain. ljbmoh@cid.csic.es
authors: Luis
authors: L
authors: Julià
authors: Jordi
authors: J
authors: Rius
authors: Xavier
authors: X
authors: Torrelles
mesh_terms: D019281:Dimerization; D004578:Electron Spin Resonance Spectroscopy; D005463:Fluoroacetates; D005609:Free Radicals / Q000138:chemical synthesis / Q000737:chemistry; D008958:Models, Molecular; D016877:Oxidants / Q000737:chemistry*; D011758:Pyrroles / Q000138:chemical synthesis / Q000737:chemistry*; D013793:Thallium; D014269:Trifluoroacetic Acid / Q000737:chemistry
chemical_list: D005463:Fluoroacetates; D005609:Free Radicals; D016877:Oxidants; D011758:Pyrroles; C054051:thallium trifluoroacetate; D013793:Thallium; D014269:Trifluoroacetic Acid