Related Experiment Video
Updated: May 8, 2026

Facile Preparation of 4-Substituted Quinazoline Derivatives
Published on: February 15, 2016
7-Hydroxyquinoline-8-carbaldehydes. 2. Prototropic equilibria
Volha Vetokhina1, Jacek Nowacki, Mariusz Pietrzak
1Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.
Abstract:
Prototropic equilibria were studied for a series of 7-hydroxyquinoline-8-carbaldehydes (7-HQCs) by (1)H NMR spectroscopy, photostationary and time-resolved UV-vis spectroscopic methods, and quantum chemical computations. These molecules represent trifunctional proton-donating/accepting systems that in aqueous solutions may assume four main neutral and ionic structures: 7-quinolinol (OH), 7(1H)-quinolinone (NH), deprotonated anion (A), and protonated cation (C). Electronic absorption and fluorescence of 7-HQCs are rationalized in terms of the ground and excited-state long-range tautomerization (part 1) as well as protonation and deprotonation processes. The photophysical properties of neutral and ionic forms of 7-HQCs are compared with those of 7-hydroxyquinolines (7-HQs), synthetic precursors of the former. The experimental results are corroborated by ab initio computations.
Related Concept Videos
Complexation Equilibria: Overview
The equilibrium constant of the complexation reaction is represented as the formation constant...
Polyprotic Acids
The Equilibrium Constant
Ladder Diagrams: Complexation Equilibria
The formation constant, K1, for the formation of Cd(NH3)2+ complex from cadmium and ammonia is 3.55 × 102. Log K1 (i.e. pNH3) is 2.55, and...
Complexation Equilibria: Factors Influencing Stability of Complexes
Chemical Equilibria: Systematic Approach to Equilibrium Calculations
The first step is to identify all the chemical reactions involved, The...

