Torsional angles in N-substituted benzamides and related compounds by carbon-13 N.M.R. chemical shifts

Abstract

The torsional angles in 30 N-substituted benzamides and related compounds have been estimated by the use of the ¹³C substituent chemical shifts of the meta and para carbon atoms. Steric interaction between the N-substituted groups and the ortho hydrogen atoms of the benzene ring is the major determinant of non-planarity in these systems. A linear relationship between steric substituent constants of the N-substituted groups of some benzamides and the torsional angles is proposed. Dynamic processes involving rotation about the C-N bond, nitrogen inversion and ring inversion contribute a dynamic steric effect to the overall steric interaction. The preferred conformations of some N-substituted groups is also discussed.