title: Ring-substituted benzohydroxamic acids: 1H, 13C and 15N NMR spectra and NH-OH proton exchange.
abstract: NMR spectra (1H, 13C, 15N) of para- and meta-substituted benzohydroxamic acids were studied in dry dimethyl sulfoxide solutions. The 13C chemical shifts were very close to those found by cross-polarization magic angle spinning in solids, the hydroxamic (not hydroximic) structure of which is unambiguous. The hydroxamic structure of these acids in DMSO solutions was proved independently by their 15N chemical shifts. The 15N and 1H chemical shifts of the NH-OH fragment showed excellent mutual dependences and dependences on the nature of the ring substituent. According to these dependences and ab initio energy calculations, all the acids assume the same Z conformation. Proton exchange between hydroxamic OH and NH groups in DMSO proceeded by both intra- and intermolecular exchange and the rates did not exhibit any simple relationship to the substituent constants.
authors.affiliation: Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, 16502 Prague 6, Czech Republic. schraml@icpf.cas.cz
authors.forename: Jan
authors.initials: J
authors.lastname: Schraml
authors.forename: Marcela
authors.initials: M
authors.lastname: Tkadlecová
authors.forename: Statis
authors.initials: S
authors.lastname: Pataridis
authors.forename: Ludmila
authors.initials: L
authors.lastname: Soukupová
authors.forename: Vratislav
authors.initials: V
authors.lastname: Blechta
authors.forename: Jana
authors.initials: J
authors.lastname: Roithová
authors.forename: Otto
authors.initials: O
authors.lastname: Exner
mesh_terms: D000465:Algorithms; D002247:Carbon Isotopes; D003198:Computer Simulation; D006877:Hydroxamic Acids / Q000032:analysis / Q000737:chemistry*; D017665:Hydroxyl Radical; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009587:Nitrogen Isotopes; D011522:Protons
chemical_list: D002247:Carbon Isotopes; D006877:Hydroxamic Acids; D009587:Nitrogen Isotopes; D011522:Protons; D017665:Hydroxyl Radical; C006696:benzohydroxamic acid