Natural-abundance nitrogen-15 nuclear magnetic resonance spectroscopy. Electronic effects in benzenesulfonamides

The ^(15)N chemical shifts of a number of benzenesulfonamides with different substituents at nitrogen have been measured in dimethyl sulfoxide solution and compared to those of similarly substituted benzenamines and ethanamides. The relative extent of phenyl-sulfur and nitrogen-sulfur p_π-d_π orbital overlap is discussed. Substitution of C_6H_5SO_2 for one benzyl group of N,N-dibenzylethanamide results in considerable lowering of the free energy of activation of the N-CO bond rotation.