1,3-dichlorobenzene. Molecular model of 1,3-dichlorobenzene, an isomer of dichlorobenzene with two chlorine atoms replacing two of the hydrogen atoms on a benzene ring. 1,3-dichlorobenzene, or m-dichlorobenzene, is a colourless liquid, which is soluble in alcohol and ether, and used to make herbicides, insecticides, medicine and dyes. Little is known about the health effects but they are likely to include eye and nose irritation, breathing difficulties and an upset stomach. Atoms are colour-coded: hydrogen (white), carbon (grey) and chlorine (green).