Ionization of carbonyl compounds in sulfuric acid. Correction for medium effects by characteristic vector analysis

Protonation acidity constants for benzotoluidides in sulfuric acid solutions

“…For a large number of carbonyl compounds [1] the absorbance at any acid concentration can be described as a mean absorbance of at least two principal components (PC). It is reasonable to associate the first PC with the effect of protonation and the second PC with the medium effect.…”

“…, independent of wavelength. When this method is used, which separates the protonation effects from medium effects, the protonation information is contained in q 1 [1,9,10]. The reconstructed spectra using the first principal components (Figure 2-4) intersect at isosbestic points.…”

“…The same ionization ratios are obtained directly from the coefficients of the first PC [1,4,9] i.e. the weighting coefficients:…”

“…Acidity constants are obtained by analysing the changes of some physical properties of the observed substrates at varying acid concentrations. The three most commonly studied properties are the observed changes in the characteristics of UV-VIS, 1 H, and 13 C NMR spectra [1][2][3][4] that occur in going from the free base to the protonated base as the acidity of the solutions increases.…”

“…Various methods have been widely employed to compensate for medium effects, e.g. principal component analysis (PCA) [5], target testing method of factor analysis [6,7], and characteristic vector analysis (CVA) [1,[8][9][10].…”