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The visible absorption band of triazolium ylids is relatively sensitive to the solvent nature and can be used to characterize the intermolecular interactions in liquid solutions. Ternary solutions of the types: methanol (1) + benzene (2) + ylid and water (1) + methanol (2) + ylid were studied by means of the visible absorption spectra. Three carbanion monosubstituted 4′-tolyl-1,2,4-triazol-1-ium-4-R-phenacylids with variable R substituent were used to evidence the specific interactions between OH group of hydroxyl solvents and the ylid carbanion. The differences between the intermolecular potential energies in pairs of the types: methanol–ylid, benzene–ylid and water–ylid were estimated in the limits of statistic cell model of ternary solutions. The average statistic weights of the two solvents in the first solvation shell of ylids (estimated on the basis of the statistic cell model of ternary solutions) were compared with the corresponding molar fractions in the bulk solution, in order to obtain information about the ternary solution homogeneity.

The dipolar compound Phthalazinium-dibenzoylmethylid (PDBM) was used as spectrally active molecule in order to analyze the molecular interactions in ternary solutions containing at least one protic solvent. In PDBM+protic solvent (1)+aprotic solvent (2) ternary solutions, PDBM can be involved both in universal and specific interactions reflected in solvatochromic effects. The protic solvent (or the solvent with the higher electric permittivity) was considered as being active from the interactions point of view. The content of the first solvation sphere of the studied ylid has been established on the basis of the statistical cell model of ternary solutions. The active solvent molecules are dominant in the first solvation sphere of the PDBM molecules. The difference between the interaction energies in the PDBM-active solvent (1) and PDBM-inactive solvent (2) molecular pairs has been determined for three binary solvents water+ethanol (W+E), propionic acid+chloroform (PA+C) and octanol+1,2 dichloroethane (O+DCE). The hydrogen bond formation energy of the PDBM-protic solvent complex has been estimated in the binary solvents PA+C and O+DCE containing one protic (PA and O, respectively) and one aprotic solvent with close electro-optical parameters refractive index and electric permittivity of the components.

The proposed method consists essentially in the treatment of an aromatic acid chloride solution with certain amounts of N-acyl-aminoacid as reagent. The mechanism of the colored chemical reaction is described here and the concentration of the aromatic acid chloride is determined on the basis of Bouguer–Lambert–Beer law. The results are discussed having in view the electrostatic interactions in the liquid solution in which the reaction takes place. The proposed method offers a high sensitivity, accuracy, easiness and quickness of the operations.