Intramolecular interactions in N1-substituted sulfanilamides (SA) can rationalize the trend of their antibacterial powers with the use of a resonance scheme, derived from d orbital symmetry and tested with an extensive spectroscopic investigation on amidic, imidic, and anionic SA. On quantitative grounds, a good relationship is presented between the antibacterial power and the proton chemical shift of the p-amino group. The electronic features for high activity are described.