HydrocarbonOrganic compound containing only carbon and hydrogen. Click on Term to Read More compounds in which the carbonElement commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*. Click on Term to Read More atoms are connected by a ring structure that is planar and joined by σ and π bonds between the carbon atoms. Examples of aromatic compounds include ethylene (IUPAC name: ethene), C2H4, and benzene, C6H6.