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An EPR analysis of β‐dimerization in α‐blocked pyrroles in oxidant conditions
Author(s) -
Julià Luis,
Rius Jordi,
Torrelles Xavier
Publication year - 2011
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2710
Subject(s) - chemistry , electron paramagnetic resonance , unpaired electron , steric effects , monomer , crystallography , resonance (particle physics) , photochemistry , stereochemistry , radical , nuclear magnetic resonance , polymer , organic chemistry , physics , particle physics
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. Copyright © 2011 John Wiley & Sons, Ltd.