title: Geometric and electronic structures of phenoxyl radicals hydrogen bonded to neutral and cationic partners.
abstract: 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.
authors.affiliation: Laboratoire de Spectrochimie Infrarouge et Raman, Bâtiment C5-UMR CNRS 8516, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Maylis
authors.initials: M
authors.lastname: Orio
authors.forename: Olivier
authors.initials: O
authors.lastname: Jarjayes
authors.forename: Benoit
authors.initials: B
authors.lastname: Baptiste
authors.forename: Christian
authors.initials: C
authors.lastname: Philouze
authors.forename: Carole
authors.initials: C
authors.lastname: Duboc
authors.forename: Jenny-Lee
authors.initials: JL
authors.lastname: Mathias
authors.forename: Laurent
authors.initials: L
authors.lastname: Benisvy
authors.forename: Fabrice
authors.initials: F
authors.lastname: Thomas
mesh_terms: D001562:Benzimidazoles / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D006860:Hydrogen Bonding; D007097:Imines / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010636:Phenols / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D001562:Benzimidazoles; D002412:Cations; D007097:Imines; D010636:Phenols; C042329:phenoxy radical