title: The hydrogen-bonded 2-pyridone dimer model system. 1. Combined NMR and FT-IR spectroscopy study.
abstract: 2-Pyridone (PD), converting to 2-hydroxypyridine (HP) through a lactam-lactim isomerization mechanism, can form three different cyclic dimers by hydrogen bond formation: (PD)(2), (PD-HP), and (HP)(2). We investigate the complexation chemistry of pyridone in dichloromethane-d(2) using a combined NMR and Fourier transform infrared (FT-IR) approach. Temperature-dependent (1)H NMR spectra indicate that at low temperatures (<200 K) pyridone in solution predominantly exists as a cyclic (PD)(2) dimer, in exchange with PD monomers. At higher temperatures a proton exchange mechanism sets in, leading to a collapse of the doublet of (15)N labeled 2-pyridone. Linear FT-IR spectra indicate the existence of several pyridone species, where, however, a straightforward interpretation is hampered by extensive spectral overlap of many vibrational transitions in both the fingerprint and the NH/OH stretching regions. Two-dimensional IR correlation spectroscopy applied on concentration-dependent and temperature-dependent data sets reveals the existence of the (PD)(2) cyclic dimer, of PD-CD(2)Cl(2) solute-solvent complexes, and of PD-PD chainlike dimers. Regarding the difference in effective time scales of the NMR and FT-IR experiments, milliseconds vs (sub)picoseconds, the cyclic dimers (PD-HP) and (HP)(2), and the chainlike conformations HP-PD, may function as intermediates in reaction pathways through which the protons exchange between PD units in cyclic (PD)(2).
authors.affiliation: Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany.
authors.forename: Łukasz
authors.initials: Ł
authors.lastname: Szyc
authors.forename: Jing
authors.initials: J
authors.lastname: Guo
authors.forename: Ming
authors.initials: M
authors.lastname: Yang
authors.forename: Jens
authors.initials: J
authors.lastname: Dreyer
authors.forename: Peter M
authors.initials: PM
authors.lastname: Tolstoy
authors.forename: Erik T J
authors.initials: ET
authors.lastname: Nibbering
authors.forename: Bogusława
authors.initials: B
authors.lastname: Czarnik-Matusewicz
authors.forename: Thomas
authors.initials: T
authors.lastname: Elsaesser
authors.forename: Hans-Heinrich
authors.initials: HH
authors.lastname: Limbach
mesh_terms: D019281:Dimerization; D006860:Hydrogen Bonding; D007536:Isomerism; D007769:Lactams / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D011728:Pyridones / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D007769:Lactams; D011728:Pyridones; D012996:Solutions; D012997:Solvents; C017679:2-hydroxypyridine