of benzene with three methyl substituent s symmetrically placed on the ring. Isomeric trimethylbenzenes include hemimellitene (1,2,3-trimethylbenzene) and pseudocumene (1,2,4-trimethylbenzene). All three compounds have the formula C 6 H 3 (CH 3 ) 3 , which is commonly abbreviated C 6 H 3 Me 3 . Mesitylene is a colourless liquid