Related Experiment Video
Updated: Jun 17, 2026

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Electronic absorption study on acid-base equilibria for some pyrimidine derivatives containing semi- and
1Department of Physical Chemistry, Faculty of Sciences and Letters, Marmara University, Ziverbey 34722, Goztepe, Istanbul, Turkey. hkilic@marmara.edu.tr
Abstract:
The UV-vis spectra of recently synthesized 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-one, (I), and 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-thione, (II) were studied in aqueous methanol (5%, v/v methanol). The nature of the electronic transitions and the roles of carbonyl oxygen of I and thiocarbonyl sulfur of II on the behavior of UV-vis spectra were discussed. Acid-base equilibria of the compounds against varying pH and pK(a) values related equilibria were determined at an ionic strength of 0.10 M by using the Henderson-Haselbalch equation. The mean acidity constants for the protonated forms of the compounds were determined as pK(a1)=5.121, pK(a2)=7.929 and pK(a3)=11.130 for I and pK(a1)=4.684, pK(a2)=7.245 and pK(a3)=10.630 for II. The preferred dissociation mechanisms were discussed based on UV-vis data and a mechanism was proposed for each compound.
Related Concept Videos
Basicity of Heterocyclic Aromatic Amines
Spectroscopy of Carboxylic Acid Derivatives
In the...
Basicity of Aromatic Amines
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
Acidity and Basicity of Carboxylic Acid Derivatives
The relative acidic strength of the derivatives can be explained based on the extent of resonance stabilization of the conjugate base. The...
Substituent Effects on Acidity of Carboxylic Acids

