NMR AND COMPUTER MODELING CONFORMATIONAL STUDY OF N-BENZYL,N-N-PROPYL(2-METHYL-3-NITROPHENYL)ACETAMIDE

The conformation of N-benzyl-N-n-propyl (2-methyl-3-nitrophenyl) aceta mide 1 in dimethyl sulfoxide (DMSO-d(s)) dr chloroform (CDCl3) solutio n was studied using H-1 and C-13 NMR analysis. In solution, 1 existed as two distinct Z and E isomers, which could not be separated at labor atory temperature. Both conformations were in equivalent proportions i n chloroform whereas in a polar solvant (DMSO), the conformation Z was more usual with the aromatic rings in a trans position. Major and min or rotation isomers were assigned from the H-1 and C-13 NMR chemical s hifts determined at 293 K. Separate treatment of signals displayed by two different methylene groups gave comparable activation parameters ( Delta G approximate to 16 kcal/mol). Conformational analysis and measu rement of the rotational barrier between the E and Z conformers by mol ecular modeling (Sybyl program) were performed.