Association and solubility of chlorophenols in CCl4: MIR/NIR spectroscopic and DFT study

This work provides new information on the effect of position and number of substituents on association and solubility of chlorophenols in CCl4. Using MIR and NIR spectroscopy we examined solutions of 12 chlorophenols at several concentrations. In addition, we calculated (DFT) theoretical spectra and struc-tures of monomers and associates of chlorophenols from dimer to tetramer. The number of substituents at positions 2 and 6 allows to divide studied chlorophenols into three Groups: I (3; 4; 3,4; 3,5), II (2; 2,3; 2,4; 2,5; 2,4,5), and III (2,6; 2,4,6; 2,3,4,5,6). An equilibrium between intermolecular OH???OH and intramolecular OH center dot center dot center dot Cl hydrogen bonding depends on position and number of substituents. The extent of association decreases in going from Group I to Group III due to growing steric hindrance near the OH group and the resonance effect from Cl. In chlorophenols of Group I, Cl at positions 3 or 5 weakens the OH center dot center dot center dot OH intermolecular hydrogen bonding, while for Group II it strengthens the OH center dot center dot center dot Cl intramolec-ular bonding. In contrast, Cl at position 4 has minor effect on association. In the case of Group I, increasing concentration shifts the equilibrium towards solute-solute interactions, whereas for Groups II and III dominate the species with intramolecular OH center dot center dot center dot Cl bonding. The theoretical calculations predict that for monosubstituted chlorophenols of Group I the most stable are non-planar cyclic tetramers, while for dis-ubstituted ones, the non-planar cyclic tetramers and linear trimers have similar binding energies. Chlorophenols of Group II prefer the cyclic non-planar trimers, whereas those of Group III form the planar dimers with an antiparallel orientation of the OH groups. Our study reveals that chlorophenols creating the cyclic associates are better soluble in CCl4 as compared with those forming the linear ones. Hence, one can conclude that in an inert or weakly interacting solvents the solubility is closely related to the struc-ture of the solute associates. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study provides new insights into the impact of position and number of substituents on the association and solubility of chlorophenols in CCl4. The research reveals that the equilibrium between intermolecular and intramolecular hydrogen bonding depends on the position and number of substituents, leading to variations in the extent of association. Theoretical calculations predict the most stable structures for different types of chlorophenols. The findings highlight the importance of solute associates' structure in determining solubility in inert or weakly interacting solvents.