cresol (krēˈsōl) [key], CH3C6H4OH, any one of three aromatic alcohols present in coal tar. The three compounds are structural isomers; they may be thought of as hydroxy derivatives of toluene or as methyl derivatives of phenol. The names of the three compounds indicate which of the hydrogens on the benzene ring portion of the molecule have been replaced. Two adjacent hydrogens are replaced, one with a methyl group and one with a hydroxyl group, to form ortho -cresol, also called 2-hydroxytoluene, or 2-methylphenol. When a single unreplaced hydrogen lies between the two that are replaced, the compound formed is meta -cresol, 3-hydroxytoluene, or 3-methylphenol. When the replaced hydrogens lie opposite one another on the ring, the compound formed is para -cresol, 4-hydroxytoluene, or 4-methylphenol. Because the boiling points of these three compounds are nearly the same, a separation of a mixture of the three into its pure components is impractical. The mixture of cresols obtained from coal tar is called cresylic acid. The cresols are used in the manufacture of disinfectants and synthetic resins.