The conformation of the amide group in N-acyl-indolines and -1,2,3,4-tetrahydroquinolines

Abstract

Studies of ¹H n.m.r. spectra at ambient and at low temperature indicated that whereas in 5-substituted N-acyl-indolines the amide group has the Z-conformation, in 6-substituted N-acetyl-1,2,3,4-tetrahydroquinolines (THQ) it assumes both Z- and E-conformations. This was confirmed by aromatic solvent-induced shifts in the n.m.r. spectra. U.v. spectroscopy suggested that the differences in the anisotropic deshielding effects of the carbonyl group observed in the two series could be explained by three being a greater divergence from coplanarity of the aromatic ring and the carbonyl group in the THQ series than in the indoline series.