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1 2009

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Hydrogen Bonds in the 1:1 and 2:1 Complexes of 1-Methylquinolinium-3-carboxylate with Mineral Acids Studied by NMR, FTIR and Raman Spectra and DFT Calculations

Barczyński P., Szafran M.

Polish Journal of Chemistry

2009

Vol. 83, nr 5

1061-1074

The 1:1 and 2:1 complexes of 1-methylquinolinium-3-carboxylate (benzotrigonelline), 3QB, with HCl, HBr, HNO3, HClO4 and HBF4 have been synthesized and their FTIR, Raman, 1H and 13C NMR spectra have been analyzed. The 1:1 complexes with HCl and HBr crystallize as monohydrates and water molecule is localized between the betaine and counter-ions (Cl– and Br–). In the complexes with HNO3, HClO4 and HBF4 the anions are connected with the protonated 3QB via O–HźźźX– hydrogen bonds. The 2:1 complexes with HCl, HBr, HNO3 and HClO4 crystallize with one water molecule while with HBF4 as an hydrous. Their FTIR spectra show a broad and intense absorption in the 1500–400 cm–1 region, typical of hydrogen bonds shorter than 2.5 A. The water molecule in the 2:1 complexes, except perchlorate, forms hydrogen bonds with anions. The influence of counter-ions on proton and carbon-13 chemical shifts is very small and comparable with the experimental error. The protonation of 3QB causes deshielding of all protons and most carbons, except C-3, C-9 and COO, which are shielded. The 2:1 complexes in D2O dissociate to the 1:1 complexes and 3QB. Five 1:1 (2–6) and six 2:1 (7–12) complexes have been analyzed by the B3LYP/6-31G(d,p) calculations in order to determine the influence of conformation of COOH groups on hydrogen bond and homoconjugation.