1H and 13C NMR studies on the self‐association of retinoic acid

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AbstractThe monomer–dimer equilibrium of retinoic acid in carbon tetrachloride was studied by 1H and 13C NMR spectroscopy. The dimer dissociation constant at 24°C was determined to be 0.38 mM from a fit of the changes in the carboxylic acid carbon chemical shift as a function of concentration. The temperature dependence of the equilibrium constant obtained from the 13C NMR signals was used to determine the enthalpy (8.0 kcal mol−1) and entropy (12 cal mol−1 K−1) changes for the dimer dissociation process. These results were shown to be more precise than the values obtained from the carboxylic acid proton resonance.