Benzene is an aromatic hydrocarbon in which the six carbon atoms are arranged in a ring, with all carbon bonds equal and intermediate in length between single and double bonds. Under standard laboratory conditions benzene is a colorless and highly flammable liquid with a sweet smell. Benzene is a known carcinogen and has various toxic effects on humans.
Benzene was first isolated by the English chemist/physicist Michael Faraday in 1825, although the natural aromatic resin that contains benzene comes from Southeast Asia and was known to Arab traders during the Middle Ages. The cyclic structure of benzene was announced in 1865 by the German chemist Friedrich A. Kekulé, with the data on carbon bond lengths coming from X-ray diffraction measurements. An astronomical detection in the protoplanetary nebula CRL 618 has been reported by Cernicharo et al. (2001) from mid-infrared observations, and the measured abundance is matched by...