Density functional theory calculations have been preformed on a series of the hydrogen-bonded fluorophenol-ammonia and bromophenol-ammonia complexes. Intermolecular and intramolecular properties, particularly those related to hydrogen bonding, have been carefully analyzed. Several properties, such as the bond length and stretching frequency of the hydroxyl group, the hydrogen bond length and binding energy, are shown to be highly correlated with each other and are linearly correlated with known experimental pKa values of the halogenated phenols. The linear correlations have been used to predict the pKa values of all fluorophenols and bromophenols in the series. The predicted pKa values are shown to be consistent from different molecular properties and are in good agreement with available experimental values. This study suggests that calculated molecular properties of hydrogen-bonded complexes allow the effective and systematic prediction of pKa values for a large range of organic acids using the established linear correlations.

Density functional theory calculations have been preformed on a series of hydrogen-bonded complexes of substituted aliphatic and aromatic carboxylic acids with ammonia. Molecular properties, particularly those related to hydrogen bonding, have been carefully examined for their interdependence as well as dependence on the acidity of the acid. The bond length and stretching frequency of the hydroxyl group and the hydrogen-bond length and energy of the complex are shown to be highly correlated with each other and are linearly correlated with available literature pKa values of the carboxylic acids. The linear correlations resulting from the fit to the available pKa values can be used to predict the pKa values of similar carboxylic acids. The pKa values so predicted using the different molecular properties are highly consistent and in good agreement with the literature values. This study suggests that calculated molecular properties of hydrogen-bonded complexes allow effective and systematic prediction of pKa values for a large range of organic acids using the established linear correlations. This approach is unique in its capability to determine the acidity of a particular functional group or the local acidity within a large molecular system such as a protein.

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.

Density functional theory and ab initio molecular orbital calculations have been carried out to investigate the molecular structures and properties of all 19 chlorophenol congeners. The results have been delineanated systematically in terms of the position and the total number of chlorine substitutions. Intramolecular hydrogen bonding in ortho chlorophenols and the induction by the electron-withdrawing chlorine are identified as strongly affecting the stability, structure, and properties of these compounds. Ortho chlorophenols are found to be more stable than other isomers as a result of intramolecular hydrogen bonding. Correlations between the known acidities of chlorophenols and the molecular structures are presented. Ortho chlorophenols are more acidic than other isomers because of the large inductive effect of chlorine on the hydroxyl group in close proximity. For the same reason, the acidity of a chlorophenol increases with the number of chlorine substitutions. Major trends and variations in molecular structure and properties, including O−H and C−O bond lengths, O−H stretching and torsional frequencies, average C−C bond lengths, and C−Cl bond lengths, are discussed in light of the intramolecular hydrogen bonding and the induction of chlorine.

A new class of luminescent cyclometalated Ir(iii) complexes with readily tunable mechanochromic properties derived from the mechanically induced trans-to-cis isomerization have been developed.