High Quality Content by WIKIPEDIA articles! Xylene encompasses three isomers of dimethylbenzene. The isomers are distinguished by the designations ortho- (o-), meta- (m-), and para- (p-), which specify to which carbon atoms (of the benzene ring) the two methyl groups are attached. Counting the carbon atoms from one of the ring carbons bonded to a methyl group, and counting towards the second ring carbon bonded to a methyl group, the o- isomer has the IUPAC name of 1,2-dimethylbenzene, the m- isomer has the IUPAC name of 1,3-dimethylbenzene, and the p- isomer has the IUPAC name of 1,4-dimethylbenzene. The mixture is a slightly greasy, colourless liquid commonly encountered as a solvent. Several million tons are produced annually.