Factor Analysis as a Complement to Band Resolution Techniques. III. Self Association in Trichloroacetic Acid

Abstract

Digitized infrared spectra of nine solutions of trichloroacetic acid in CCl₄ have been studied in the carbonyl stretching region. At all concentrations only two bands are visually apparent. However, factor analysis indicates the presence of four absorbing components. The contour resolution technique gives a monomer band at 1786 cm⁻¹, a dimer band at 1749 cm⁻¹, and a third band close to the dimer frequency at approximately 1735 cm⁻¹. Examination of the changes in Cauchy–Gauss shape ratio of the monomer band with increasing concentration indicates the presence of an unresolved component. The band at 1735 cm⁻¹ and the unresolved band near the monomer peak at 1786 cm⁻¹ are assigned to absorption of carbonyl groups in linear polymers of trichloroaceticacid. The monomer–dimer equilibrium constant was calculated from the molar absorption coefficients and absorbances of monomer and dimer bands. The average value over the concentration range 0.305 × 10⁻³ to 0.1603 M was 287 l/mol at 33.9 ± 0.5 °C.