Effects of aqueous alcohol and other non-electrolyte solutions on the thermal perturbation spectra of aromatic compounds

Abstract

Difference spectrophotometry of identical solutions of aromatic compounds at different temperatures results in thermal perturbation difference spectra. These difference spectra were examined over the wavelength range 350-240 nm in water and in aqueous solutions of alcohols, ethylene glycol, dioxane, dimethyl sulphoxide, urea and tetramethylurea. The longest wavelength difference extremum has a positive Δε/ΔT(change in molar extinction coefficient with temperature) which exhibits maxima at concentrations of alcohols similar to the maxima and minima shown by other properties of aqueous alcohol solutions. The more apolar the cosolvent the larger the value of Δε/ΔT at the maximum and the smaller the mol fraction at which the maximum occurs. The results are attributed largely to changes in water-cosolvent interactions that are also observed by other physico-chemical methods.