Effect of solvent media and condensed benzene rings on thermochemical behaviour of dibenzo-18-crown-6 in solution

Enthalpies of solution of dibenzo-18-crown-6 at infinite dilution have been measured in tetrachloromethane, benzene, chloroform, pyridine, acetone, dimethylformamide, dimethylsulfoxide, acetonitrile, benzyl alcohol and propylene carbonate at temperature of 298.15 K. Values for enthalpy of solvation and solute–solvent interaction in the solvents were determined. Correlation of enthalpies of solvation with the enthalpy of cavity formation and contribution for the different types of solute–solvent interaction was obtained. In benzene, tetrachloromethane, pyridine, DMF and DMSO polar conformer of DB18C6 dominates. Its effective dipole moment amounts to 3.7 D. Conformation dynamics of the solute reduces the effective polarity of such solvents as acetone, chloroform and propylene carbonate in which population of polar conformer of dibenzo-18-crown-6 decreases. Condensation of two benzene rings to 18-crown-6 results in increasing molecule polarity and exothermic contribution of dipole–dipole interaction in polar solvent media. The specific interaction with acetonitrile and chloroform becomes weaker from 18-crown-6 to dibenzo-18-crown-6.