Cis-trans-isomerism of the Protonated Ring-substituted Acetanilides

Abstract

The cis-trans-isomerism of the protonated ring-substituted acetanilides in CF₃COOH has been investigated by measurements of the intensity ratio of the methyl signals in acetylamino groups in their ¹H-NMR spectra at 30°C. Consequently, the acetanilides with an electrondonative group and monohaloacetanilides (Group I) showed the cis-trans-isomerism, and their equilibrium ratios (EIZ) were found to be about 1/4∼1/7 in CF₃COOH. And then, the acetanilides with nitro group as an electron-attractive group (Group II) showed only Z-form. In the cases of 2, 6-dihaloacetanilides (Group III), both E- and Z-isomers were observed, whose E/Z ratios were obtained to be about 1/3∼1/5 in CF₃COOH. Furthermore, the activation parameters of the equilibrium between E- and Z-forms in Group III were obtained by the line-shape analysis of their DNMR spectra in CDC₃ or CF₃COOH (e. g., 2, 6-dichloroacetanilide [1n] _??_=68.1 kJ/mol, _??_=63.5 kJimol; K (E/Z)=1/7 in CDCl₃ at 25°).