Showing papers by "Maciej J. Nowak published in 2007"
TL;DR: The combined experimental and theoretical results reveal links between aromaticity and tautomerism and a UV-induced phototautomeric reaction transforming the oxo forms into the hydroxy tautomers was observed for all (except 3-hydroxyisoquinoline) studied compounds.
Abstract: Oxo−hydroxy tautomerism and phototautomerism of 2-quinolinone, 1-isoquinolinone, 3-hydroxyisoquinoline, 2-quinoxalinone, and 4-quinazolinone were studied using the matrix-isolation technique. These compounds contain a benzene ring fused with a heterocyclic ring of 2-pyridinone, 2-pyrazinone, or 4-pyrimidinone. It turned out that direct attachment of a benzene ring to a heterocycle leads to a very pronounced increase of the relative stability of oxo tautomers (in comparison with the tautomerism of the parent compounds 2-pyridinone, 2-pyrazinone, and 4-pyrimidinone). The only exception concerns 3-hydroxyisoquinoline, where fusion with a benzene ring enforces rearrangement of the double- and single-bond system in the oxo tautomer. This destabilizes substantially the oxo form with respect to the hydroxy tautomer. The ratios of population of the oxo and hydroxy tautomers observed in Ar matrixes correspond to the tautomeric equilibria of the compounds in the gas phase. These equilibria were well reproduced by t...
64 citations
TL;DR: All isomers were identified by comparing their experimental IR spectra with the spectra theoretically calculated at the DFT(B3LYP)/6-31G(d,p) level, where DFT is the density functional theory and good agreement between the observed and predicted patterns of the spectral lines allowed for reliable identification.
Abstract: Infrared spectra of N4-hydroxycytosine isolated in argon and nitrogen low-temperature matrixes are reported. The compound was found to adopt the syn structure of the imino-oxo tautomeric form exclusively. A photoreaction (λ > 250 nm) converting this form into the anti isomer was observed. The reaction is reversible and leads to a photostationary point. The initial infrared spectrum and the spectrum of the photoproduct were assigned to the syn and anti isomers, respectively. This assignment is based on a close agreement between the experimental spectra and the spectra theoretically simulated at the DFT(B3LYP)/6-31++G** level of theory.
4 citations