Induced circular dichroism. Part II. Induced circular dichroism of the 2-benzoylbenzoic acid–amphetamine system in ethereal solvents

Abstract

Solvent effects on the induced circular dichroism (i.c.d.) of 2-benzoylbenzoic acid–amphetamine (1 : 1 salt) were investigated for various ethers and indicated that there is a strong dependence on the nature of the solvent. The strength of the i.c.d. effect in di-isopropyl ether and di-n-butyl ether, which are weakly polar and very poor cation-solvating media, was extremely large whereas in powerful cation-solvating media such as tetrahydrofuran and oxetan it was greatly reduced. The strength of the i.c.d. effect is strongly dependent on the polarity, basicity, and steric nature of the solvents. From these results, it is concluded that only the contact ion-pair of the salt exhibits large i.c.d. The i.c.d. of the solvent-separated ion-pair decreases rapidly on increasing the solvation number of the solvent. Therefore, solvent effects on the i.c.d. of the salt originated from changes in the ion-pair equilibria. Temperature effects on the i.c.d. were also examined.