| Popis: |
The title compounds (Scheme 1, Y = NMe2) were investigated by variable-temperature NMR and/or by racemization of enantiomers enriched by liquid chromatography on microcrystalline triacetylcellulose. For several reasons, a dialkylamino and a dimethylcarbamoyl group were used, for the first time, as neighboring rotor substituents on a benzene ring. Barriers to rotations about their aryl-nitrogen and/or aryl-carbon bonds were determined and assigned (Table I). Correlated or uncorrelated motions of these groups are possible for amides 11 and 19 bearing in their 3-positions tert-butyl substituents which hinder the aryl-nitrogen rotation. Uncorrelated rotations have been found for amide 15 (Figure 2) and thioamide 8 which have the less voluminous bromine atom in their 3-position. |
