A Thermodynamic Study of Infrared Spectroscopy of the Association of 2-Quinolone, Some Carboxylic Acids, and the Corresponding 2- Quinolone-acid Mixed Dimers.
Self-association of 2-quinolone in carbon tetrachloride was studied by infrared spectroscopy, using the absorption bands in the amide nh and carbonyl stretching regions. 2-Quinolone forms a cyclic dimer from which the enthalpy (ah deg., Kcal/mol), free energy (ag deg. 22, Kcal/mol), and entropy (as deg., Eu) of association are -8.69, - 6.11, and -8.76, Respectively. Dimer formation is via a carbonyl- hydrogen bond, although evidence exists for the formation of a small amount of dimer via a -hydrogen bond. 2-Quinolone was also found to form cyclic mixed dimers with carboxylic acids. Mixed dimers of 2-quinolone with benzoic, cyclohexanecarboxylic, and 4- cyclohexylbutanoic acids gave ah deg. Values of -12.2, -10.3, and - 10.4; Ag deg.22 Values of -6.36, -5.94, and -5.78; and as deg. Values of -19.9, -14.8, and -15.6, Respectively. Thermodynamic data on the acid dimers and spectral data on the different systems studied are also reported. The 2-quinolone-carboxylic acid interaction is of importance because of the simultaneous occurrence of quinolones and carboxylic acids in many biologically derived materials.
J. Phys. Chem, V. 75, No. 8, 1971, PP. 1129-1135