Illustrated Glossary of Organic Chemistry

Electrostatic potential map: A map which shows the attractive or repulsive force felt by a fixed charged (often a point positive charge, i.e., a proton) at various points in space that are equidistant from a molecular surface. Can be interpreted as a map of regions of electron excess and electron deficiency.

Electrostatic potential maps. Red = electron excess; blue = electron deficiency. Note the similarity in shape, size, and charge distribution of these molecules. PABA (p-aminobenzoic acid) is the natural substrate for a folic acid synthesis enzyme. Sulfanilamide is also accepted by this enzyme because of its similarity in size, shape, and charge distribution to PABA, but sulfanilamide inhibits this enzyme, causing its antibiotic effect.