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The study is mainly concerned with the physical factors affecting on association of carboxylic acids such as type of solvent, isomers, conjugation and steric effect of acid. The degree of association of carboxylic acid is depend on the type of cis or trans isomer of acid. It is also increased by either increasing the number of conjugated double bonds or by introducing a polar group, taking into consideration a planer structure of acid. Cis isomers of carboxylic acids prevent the association process by formation of acid monomers, while trans isomers facilitate the formation of dimers or polymers. Finally exchange of solvent from non polar (benzene) to polar (nitrobenzene), prevents the association process by formation of monomers.

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This research includes the preparation of aromatic azoimine complexes resulting from the coupling reaction (4) of Schiff bases with diazotized dinitroaniline reagent. Ultraviolet spectra, infrared spectra, and melting points are among the most important physical methods used to identification the right compounds prepared in this study. After that, the stoichiometric ratios of the components of the complex were determined using the molar ratio method, and we got a ratio of (1:1) for all the studied complexes. Finally, the factors that affect the stability constant values were studied, namely:A-Effect of acidity function: These stability constants were studied for each of the prepared complexes at each acidic function (pH) and different temperatures, and we obtained values for the stability constants, which are evidence of the preparation of stable azo complexes. B-The effect of temperature: These stability constants were calculated at a range of temperature (313-273 o K) which allowed us to know that the reactions of formation of azo dyes are spontaneous and exothermic from the negative values of (∆G o and ∆H) respectively, as well as the negative (∆S o ) value that supports what was mentioned previously. C-Effect of Structure: The type of functional group and its location also has an effect on the values of the stability constants of the prepared complexes, and this was proved by the variation in the values of the stability constants.

A b s t r a c t A r t i c l e I n f oIn this study, the study included the calculation of fourteen ionic and aromatic compounds, which included eight oximes and six Schiff bases. The parameters of the ionization of the compounds under study were calculated at absolute temperature (293K) using molecular modeling programs. Methods that included semi-empirical calculations were AUSTEN MOMEL 1 (AM1), Hatree Fock (HF), and Density functional theory (DFT). The polarizable conductor calculation model (CPCM) was used to calculate the physical variables in the solution phase instead of the gas phase using ethanol as a solvent. The ionization constants were calculated using multiple Linear regression (MLR) analysis and using various descriptive variables selected to test their representatively of the observed variation in pK a values These variables include a Mullikan charge on the atoms of the hydroxyl and azomethine group (C = N), the length of the double bond, the angles values, the value of the fixed dipole moment, DIHADRAL, the total energy and the heat of the formation temperature), molecular properties such as HOMO, LUMO, Molecular hardness, electrolyte guide and chemical potential. These values were correlated with pKa values. In this relationship, the values of pK a were calculated theoretically. The results obtained showed that the HF method and the AM1 method were preferable to the EDP method, although all methods were able to complete this type of calculation And with a good efficiency in describing the effect of substituents on pK a values, these results were clearly indicated by the high correlation coefficients (R 2 ) obtained from the regression analysis and the correlation between the practical values of pKa and those calculated theoretically.