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Geometric and Electronic Structures of Phenoxyl Radicals Hydrogen Bonded to Neutral and Cationic Partners
Author(s) -
Orio Maylis,
Jarjayes Olivier,
Baptiste Benoit,
Philouze Christian,
Duboc Carole,
Mathias JennyLee,
Benisvy Laurent,
Thomas Fabrice
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102854
Subject(s) - chemistry , intramolecular force , moiety , intermolecular force , hydrogen bond , electron paramagnetic resonance , cationic polymerization , tautomer , radical , photochemistry , crystallography , stereochemistry , medicinal chemistry , molecule , organic chemistry , nuclear magnetic resonance , physics
Two di‐ tert ‐butylphenols incorporating an N ‐methylbenzimidazole moiety in the ortho or para position have been synthesised ( Me OH and pMe OH, respectively). Their X‐ray structures evidence a hydrogen bond between the phenolic proton and the iminic nitrogen atom, whose nature is intra‐ and intermolecular, respectively. The present studies demonstrate that Me OH is readily oxidised by an intramolecular PET mechanism to form the hydrogen‐bonded phenoxyl‐ N ‐methylbenzimidazolium system ( Me OH) . + , whereas oxidation of pMe OH occurs by intermolecular PET, affording the neutral phenoxyl benzimidazole ( pMe O) . system. The deprotonations of Me OH and pMe OH yield the corresponding phenolate species ( Me O) − and ( pMe O) − , respectively, whilst that of the previously reported H OH (analogous to Me OH but lacking the N ‐methyl group) produces an unprecedented hydrogen‐bonded phenol benzimidazolate species, as evidenced by its X‐ray structure. The latter is believed to be in equilibrium in solution with its tautomeric phenolate form, as suggested by NMR, electrochemistry and DFT studies. The one‐electron oxidations of the anions occur by a simple ET process affording phenoxyl radical species, whose electronic structure has been studied by HF‐EPR spectroscopy and DFT calculations. In particular, analysis of the g 1 tensor shows the order 2.0079>2.0072>2.0069>2.0067 for ( Me O) . , ( H O) . , ( Me OH) . + and ( H OH) . + , respectively. ( Me O) . exhibits the largest g 1 tensor (2.0079), consistent with the absence of intramolecular hydrogen bond. The g 1 tensor of ( H O) . is intermediate between those of ( Me OH) . + and ( Me O) . ( g 1 =2.0072), indicating that the phenoxyl oxygen is hydrogen‐bonded with a neutral benzimidazole partner.