The analysis of the IR carbonyl band of the N, N-diethyl-2-[(4′-substituted) phenylsulfonyl] acetamides Et2NC (O) CH2S (O) 2C6H4Y (Y= OMe 1, Me 2, H 3, Cl 4, Br 5, NO26) supported by B3LYP/6-31G (d, p) calculations for 3, indicated the existence of three pairs (anti and syn) of cis (c) and gauche (g1 and g2) conformers in the gas phase, being the gauche conformers significantly more stable than the cis ones. The anti geometry is more ...