Effect of the pH of the medium on the chemical shifts in the PMR spectra and on the distribution of the π-electron density
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The dependence of the chemical shifts of the ring protons on the pH of the medium for a number of 4-hydroxyquinoline derivatives was studied by means of PMR spectroscopy. The dipolar and uncharged hydroxy forms exist in equilibrium in aqueous solutions. The effect of intramolecular hydrogen bonding on the character of the dependence of the chemical shift on the pH of the medium in the case of 3-piperidinomethyl-4-hydroxyisoquinoline was investigated. The possibility of the separate protonation of the ring nitrogen and the side-chain nitrogen in 3-piperidinomethyl-4-hydroxyisoquinoline was established. The distribution of the π-electron density in 4-hydroxyisoquinoline is in good agreement with its chemical behavior.
KeywordsHydrogen Nitrogen Spectroscopy Aqueous Solution Hydrogen Bonding
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