1) Benzene and its derivatives.
2) Hydrocarbon compounds in which the carbon atoms are connected by a ring structure that is planar and joined by sigma and pie bonds between the carbon atoms. An example of an aromatic compound is benzene, C6H6.source: [American Industrial Hygiene Association Journal; v58n9; 661-66; 1997.] [Chemistry The Central Science; Brown, Theodore; Lemay, H. Eugene; Bursten, Bruce; pp. 970-72; 1994; Prentice Hall; Englewood Cliffs, New Jersey.]