High Quality Content by WIKIPEDIA articles! There are three isomers of toluidine, which are organic compounds. These isomers are o-toluidine, m-toluidine, and p-toluidine. The o- stands for ortho- , m- stands for meta- , and p- stands for para- . All three are aryl amines whose chemical structures are similar to aniline except that a methyl group is substituted onto the benzene ring. The difference between these three isomers is the position where the methyl group (-CH3) is bonded to the ring relative to the amino functional group (-NH2); see illustration of the chemical structures below.