title: NMR and IR Investigations of Strong Intramolecular Hydrogen Bonds.
abstract: For the purpose of this review, strong hydrogen bonds have been defined on the basis of experimental data, such as OH stretching wavenumbers, νOH, and OH chemical shifts, δOH(in the latter case, after correction for ring current effects). Limits for O-H···Y systems are taken as 2800 > νOH> 1800 cm-1, and 19 ppm > δOH> 15 ppm. Recent results as well as an account of theoretical advances are presented for a series of important classes of compounds such as β-diketone enols, β-thioxoketone enols, Mannich bases, proton sponges, quinoline N-oxides and diacid anions. The O···O distance has long been used as a parameter for hydrogen bond strength in O-H···O systems. On a broad scale, a correlation between OH stretching wavenumbers and O···O distances is observed, as demonstrated experimentally as well as theoretically, but for substituted β-diketone enols this correlation is relatively weak.
authors.affiliation: Department of Science and Environment, Roskilde University, Universitetsvej 1, P.O. Box 260, DK-4000 Roskilde, Denmark. poulerik@ruc.dk.
authors.forename: Poul Erik
authors.initials: PE
authors.lastname: Hansen
authors.affiliation: Department of Science and Environment, Roskilde University, Universitetsvej 1, P.O. Box 260, DK-4000 Roskilde, Denmark. spanget@ruc.dk.
authors.forename: Jens
authors.initials: J
authors.lastname: Spanget-Larsen
mesh_terms: D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011789:Quantum Theory
chemical_list: D006859:Hydrogen
keywords: OH chemical shifts; OH stretching wavenumbers; O···O distances in O–H···O systems; Wiberg bond indices; hydrogen bond strength; isotope effects; tunneling splitting