Geometric and electronic structures of phenoxyl radicals hydrogen bonded to neutral and cationic partners

Maylis Orio, Olivier Jarjayes, Benoit Baptiste, Christian Philouze, Carole Duboc, Jenny Lee Mathias, Laurent Benisvy, Fabrice Thomas

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13 Scopus citations


Two di-tert-butylphenols incorporating an N-methylbenzimidazole moiety in the ortho or para position have been synthesised ( MeOH and pMeOH, 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 MeOH is readily oxidised by an intramolecular PET mechanism to form the hydrogen-bonded phenoxyl-N-methylbenzimidazolium system ( MeOH) .+, whereas oxidation of pMeOH occurs by intermolecular PET, affording the neutral phenoxyl benzimidazole ( pMeO) . system. The deprotonations of MeOH and pMeOH yield the corresponding phenolate species ( MeO) - and ( pMeO) -, respectively, whilst that of the previously reported HOH (analogous to MeOH 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 ( MeO) ., ( HO) ., ( MeOH) .+ and ( HOH) .+, respectively. ( MeO) . exhibits the largest g 1 tensor (2.0079), consistent with the absence of intramolecular hydrogen bond. The g 1 tensor of ( HO) . is intermediate between those of ( MeOH) .+ and ( MeO) . (g 1=2.0072), indicating that the phenoxyl oxygen is hydrogen-bonded with a neutral benzimidazole partner.

Original languageEnglish
Pages (from-to)5416-5429
Number of pages14
JournalChemistry - A European Journal
Issue number17
StatePublished - 23 Apr 2012


  • density functional calculations
  • electron transfer
  • electronic structure
  • hydrogen bonds
  • phenoxyl radicals


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