Hydrogen bonding Part 44 Thermodynamics of complexation of 3,5-dichlorophenol with ketones and ethers in cyclohexane: the Badger–Bauer relationship

Abstract

Equilibrium constants for 1:1 hydrogen bond complexation between 3,5-dichlorophenol (DCP) and 17 ketones and 12 ethers in cyclohexane solution have been obtained by an FTIR method that takes into account both dimerization of the acid and formation of 2:1 complexes. Enthalpies of complexation for the same ketones and ethers have been determined by a calorimetric method, leading to values of log K, ΔG°, ΔH° and ΔS° for 1:1 complexation in the 29 systems, as well as log K₂ for the 2:1 complexation between 2 mol of acid and 1 mol of base. For the ketone systems there is very little variation in the three thermodynamic parameters with alkyl substitution, but for the ethers there are systematic variations depending on the alkyl substituent or if the ethers are cyclic.

Values of the OH stretching frequency in the DCP complexes with the ketones and ethers in cyclohexane have been obtained. The band shapes for the DCP–ketone complexes are very asymmetric, possibly due to the presence of stereoisomeric complexes, but the ν_OH band for DCP–ether complexes is symmetric and very suitable for the evaluation of any relationship between ν_OH and ΔH°. It is found that for the complexation of DCP with the 12 aliphatic ethers in cyclohexane, there is almost no connection between the calorimetrically determined ΔH° values and values of Δν_OH.