title: Nitroxide radicals as hydrogen bonding acceptors. An infrared and EPR study.
abstract: The equilibrium constants for the formation of hydrogen-bonded complexes with phenol, benzyl alcohol and diphenyl amine of a persistent nitroxide radical (TEMPO) have been measured for the first time by IR spectroscopy in solution. By making use of the data obtained with IR measurements it was possible to quantitatively determine the effect of hydrogen bonding on the nitrogen hyperfine-splitting constant. On this basis it is shown that EPR spectroscopy can be used as an alternative to IR spectroscopy for the determination of the thermodynamic parameters of hydrogen bond formation with nitroxides by following the dependence of the experimental EPR nitrogen hyperfine splitting of these radicals upon changing the nature of the solvent. The experimental data obtained from both IR and EPR spectroscopy indicate that nitroxides are versatile hydrogen bond acceptors giving hydrogen bonds of strength similar to that of ethers or esters. The corresponding Abraham's beta 2H values have been determined as 0.46.
authors.affiliation: Dipartimento di Chimica Organica A. Mangini Università di Bologna Via S. Donato 15, 40127 Bologna, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Franchi
authors.forename: Marco
authors.initials: M
authors.lastname: Lucarini
authors.forename: Pamela
authors.initials: P
authors.lastname: Pedrielli
authors.forename: Gian Franco
authors.initials: GF
authors.lastname: Pedulli
mesh_terms: D000438:Alcohols / Q000737:chemistry; D000975:Antioxidants / Q000737:chemistry; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D006860:Hydrogen Bonding; D007700:Kinetics; D009589:Nitrogen Oxides / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013113:Spin Labels
chemical_list: D000438:Alcohols; D000975:Antioxidants; D003497:Cyclic N-Oxides; D009589:Nitrogen Oxides; D013113:Spin Labels; C039900:nitroxyl; C003959:TEMPO