Abstract
Abstract Ultraviolet absorption and Raman spectra of p-nitroaniline (pNA) have been measured in acetonitrile/CCl4 mixed solvents for seventeen different fractions of acetonitrile. The observed spectral changes were interpreted with the use of a combined singular value decomposition (SVD) analysis, in which the ultraviolet absorption and Raman spectra were combined into one set of spectra. A least-squares fitting analysis was carried out for the SVD decomposed spectra and their amplitudes, using a model in which three distinct species of pNA, the 1 : 0, 1 : 1, and 1 : 2 species, exist in equilibrium. Here, the 1 : 0, 1 : 1, and 1 : 2 species have 0, 1, and 2 acetonitrile molecules associated with pNA. Three intrinsic ultraviolet absorption and Raman spectra have been obtained as a result of the fitting analyses. The three intrinsic spectra show different degrees of charge transfer in the three different solvated forms of pNA. Two equilibrium constants, K1 for the equilibrium between the 1 : 0 and 1 : 1 species and K2 for 1 : 1 and 1 : 2, have been determined. These equilibrium constants give the standard free energy changes for the association of acetonitrile with pNA. A microscopic and quantitative view on the solvation of pNA in acetonitrile/CCl4 mixed solvents has thus been established.
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