Spectroscopic studies of long chain fatty acids. Pyridine—fatty acid—carbon tetrachloride system

Fatty acids undergo self-association and form 1:1 molecular complexes with pyridine on mixing the ingredients in the low dielectric solvent carbon tetrachloride. Infra-red spectroscopic studies of the pyridine—fatty acid—carbon tetrachloride system confirm the existence of a tautomeric equilibrium involving the ion-paired and non-ion-paired associated complexes in the solution as is represented below:

The dimerization constants (K_D) for the dimerization equilibria of palmitic and myristic acids in carbon tetrachloride have been estimated by a new method as K_D = 1·34 ± 0·2 × 10³ mole⁻¹ l (palmitic acid) K_D = 1·28 ± 0·2 × 10³ mole⁻¹ l (myristic acid).

The present study has given the following values for the equilibrium constants of the above equilibria (1).

Palmitic acid Myristic acid K₁ = 4·6 ± 0·5 K₁ = 3·6 ± 0·5 K₂ = 2·6 ± 0·5 K₂ = 2·0 ± 0·5 K_T = 0·57 K_T = 0·56

The presence of two species of the complex can be explained in terms of a double potential energy curve for the hydrogen bond system.