Electrostatic potential mapped on the surface of 2,6-dibromo-4-nitroaniline (DBNA) molecular electron density (0.001 e au?3). Color ranges for V S(r), in kcal?mol?1: red > 26.5, yellow 26.5–5.7, green 5.7– ?15.1, blue < ?15.1. Black circles Surface maxima, blue surface minima