Solvent effects on infrared frequencies—II: The effects of chloroform and carbon tetrachloride on the carbonyl bands of ketones

Abstract

The carbonyl bands of acetone and cyclohexanone were studied in pure cyclohexane and chloroform and in various mixtures of the two solvents. Some of the mixtures were studied at temperatures ranging from +27 to −55°C. The results show that chloroform forms two specific complexes with each of the ketones and that these interactions are responsible for the largest part of the observed frequency shifts. One of the complexes is of the 1:1 type, and the other one is probably a 1:2 complex in which both molecules of chloroform are hydrogen-bonded to the carbonyl group. The formation constants of the 1:1 complexes at 30°C are 1·2–0·3 1/mole. Cyclohexanone was also studied in mixtures of carbon tetrachloride and cyclohexane. The results indicate that a weak specific interaction between carbon tetrachloride and the ketone is responsible for about one-half of the total frequency shift observed in this solvent system. The relations between the results of this study and those obtained by other workers using two-component mixtures of the ketones with chloroform are discussed briefly.