Intermolecular vibrations of jet-cooled (2-pyridone)2: A model for the uracil dimer

2(1H)-pyridinone (2-pyridone): self-association and association with water. Spectral and structural characteristics: infrared study and ab initio calculations

DFT calculations of 2(1H)-pyridinone (2-pyridone NHP), the centrosymmetric dimer (NHP)2 and the closed complexes (NHP, H2O) and (NHP, 2H2O), with their deuterated homologues NDP, (NDP)2, (NDP, D2O) and (NDP, 2D2O), are compared with vibrational spectra of NHP and NDP in ternary mixtures CH3CN, NHP, H2O. Experimental data are also obtained for NHP or NDP in various solvents. The protic solvent effects demonstrate that mechanical couplings are different in the 1500-1700 cm(-1) range for the nuC=O and nu8b (valence of the ring) modes in NHP and NDP (or (NHP, H2O) and (NDP, D2O)). For the first time, data are obtained for NDP in the dimer (NHP, NDP). Comparison of data for pyridone, monomer, dimer or complexed with water, shows that in the complexes, water is a weaker proton acceptor and a stronger proton donor than a second pyridone molecule in the centrosymmetric dimer.

Hydrogen bond vibrations of 2-aminopyridine.2-pyridone, a Watson-Crick analogue of adenine.uracil

The 2-aminopyridine.2-pyridone complex (2AP.2PY) is linked by antiparallel N-H.O=C and N-H.N hydrogen bonds, providing a model for the Watson-Crick hydrogen bond configuration of the adenine-thymine and adenine-uracil nucleobase pairs. Mass-selected S(1) <--> S(0) vibronic spectra of the supersonically cooled 2AP.2PY base pair analogue were measured by laser resonant two-photon ionization and emission spectroscopies. The hydrogen bond vibrations nu(2) (buckle, out-of-plane) and the three in-plane vibrations nu(3) (opening), nu(5) (shear), and nu(6) (stretch) were observed in the S(0) and S(1) states, giving detailed information on the stretching and deformation force constants of the (amide)N-H.N(pyridine) and the (amino)N-H.O=C hydrogen bonds. Density functional calculations with the B3LYP functional and the 6-311++G(d,p) and 6-311++G(2d,2p) basis sets yield ground-state hydrogen bond frequencies in close agreement with experiment.

Crystal structure and spectral considerations of 5-methyl-2-nitraminopyridine N-oxide

The crystal structure of 5-methyl-2-nitraminopyridine N-oxide (5M) has been determined and its electronic absorption spectra in the solution have been investigated. In the solid, two monomeric proton-transferred (PT) units of 5M are perpendicularly located in the crystal lattice. They are connected by two intermolecular hydrogen bonds of different strength (O-H···N 2.647(3) and 2.695(3) Å). In the gas phase the same relative arrangement of both 5M (PT) monomers has been found. As results from semiempirical PM3-CI calculations (12–14), the prototropic amino (H) [Formula: see text] imino (PT) equilibrium may occur in the solution. Assignment of experimental absorption bands to the calculated transition energies of both forms of 5M reveals that hydrogen bonded 5M (PT) dimers are dominant in cyclohexane while imino (PT) monomers seem to prevail in acetonitrile solution. The different character of electronic transitions and different relative arrangement of both monomers in amino (H) than in imino (PT) dimers are responsible for very low oscillator strengths and dipole moments of the former.Key words: crystal structure, methylated nitraminopyridine N-oxides, semiempirical PM3-CI computations, intermolecular hydrogen bonding.

Influence of intermolecular hydrogen bonds on the tautomerism of pyridine derivatives

The effect of the dimerization, by hydrogen-bond (HB) complexation, on the tautomerism of 2-hydroxypyridine and a series 2-aminopyridines has been carried using ab initio methods. The results obtained for 2-hydroxypyridine fit satisfactorily with the experimental data and show that the 2-pyridone/2-pyridone homodimer complex is the most stable. For 2-aminopyridines, the effect of the substituent on the amino group has been investigated. For the monomers studied, the most favorable tautomer is the 2H; however, with electronegative substituents, the 1H/1H homodimers are more stable than the corresponding 2H/2H ones. The atom in molecule methodology has been used to characterize the HBs formed. Exponential relationships have been found between the electron density and its laplacian at the HB critical point vs the HB distance.