Secondary steric effects in piperidinodebromination of some 2-bromo-4-R-5-nitrothiophene-3-carboxamides in methanol

Abstract

The rates of piperidinodebromination of some N-substituted 2-bromo-4-R-5-nitrothiophene-3-carboxamides (R = H and Me) have been measured in methanol. The kinetic data obtained, as well as the investigation of the restricted rotation about the C–N bond of the amino group of some of the above carboxamides by dynamic n.m.r. spectroscopy, have shown the occurrence of steric interactions which force the 3-carboxamido group to rotate about its bond with the aromatic ring. This causes a reduced activation and a kinetic secondary steric effect.