Fig. 1. Electrostatic potential maps of isoflurane and enflurane.  Red is negative and  blue is positively charged molecular surface. Note the different position of the largest contributor to the electrostatic potentials, the chlorine. These maps were obtained from  http://www.ps.toyaku.ac.jp/dobashi(accessed February 10, 2004). Enflurane: 2-chloro-1,1,2-trifluoroethyl difluoromethyl ether; isoflurane: 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether.