Theoretical Study of Hydrogen-Bonded Complexes of Chlorophenols with Water or Ammonia:  Correlations and Predictions of pK_a Values

Abstract

A simple practical method for predicting the acidity constants (as pKa values) of chlorophenols is proposed based on density functional theory calculations of a series of hydrogen-bonded complexes of phenol and 19 different congeners of chlorophenol, with a single probe molecule, either water or ammonia. Relevant structural parameters and molecular properties of these complexes, primarily involving the acidic hydroxyl group, are examined and plotted against the known pKa values of 14 chlorophenols and phenol. Strong linear correlations are found for these compounds. Such correlations are used to determine the pKa values of five chlorophenols whose experimental acidities have large uncertainties. Similar predicted pKa values are obtained by using different structural parameters and molecular properties for the complexes with either probe molecule. The study may be extended to determine the acidity of other compounds with a single acidic functional group.

The Hammett correlation between distyrylbenzene substituents and chemiluminescence efficiency providing various ρ-values for peroxyoxalate chemiluminescence of several oxalates

“…The salient feature of these ρ-values is that the highly activated DNPO had the highest absolute ρ-values, but two oxalates, TCPO and 2,6-DCPO, had the lowest values. Because the pKa values of the phenols [43,44] are the tentative indicators of their electronic nature, the pKa of the phenols forming the oxalates (Table 1) are also related to the ρ-values as shown in Fig. 4, in which the oxalates consisting of strongly acidic phenols tend to produce high absolute ρ-values except for TCPO and 2,6-DCPO.…”

Solubility of silybin in aqueous hydrochloric acid solution

“…As indicated by Han et al [15], the pK a is well correlated with their O H bond length of their water complex. By correlating pK a and r(O H) of phenol and methoxy-phenol, Eq.…”

“…The stopped tubes were rotated for 60 h in water baths at the temperature of 293. 15 [10]. After 60 h, the rotation was stopped and the saturated solutions were kept still for 2 days at the equilibrium temperature to ensure the solid to be deposited.…”

“…These changes in molecular parameters derived from the hydrogenbonded complexes may strongly correlate with acidity and indicate the relative strength of that acid. Recently, Han et al [15] studied some hydrogen-bonded complexes involving phenol with water and ammonia. They found that several molecular parameters resulting from the phenol-water and ammonia complexes, such as the O H bond lengths, the O H stretch vibration frequencies, the hydrogen-bond lengths correlated reasonably well with the acidity of phenols in the liquid phase.…”

Adsorption of phenolic compounds on some hybrid xerogels

“…This peak also shows a shoulder at 297 nm which is assigned to the anionic form of dCP. Considering the relatively high pK a of dCP [17], it is assumed that the equilibrium between dCP and its corresponding anion shifts largely toward the anion in the presence of the HyXs which, in turn, causes the observed blue shift in its UV-vis spectrum that would explain the increase in absorbance observed. This would suggest that there is an acid-base interaction between the xerogels and dCP supporting the idea that the prepared xerogels and HyXs bear negative charges [4,18].…”