Annulenes
Annulenes are cyclic compound, monocyclic hydrocarbons that contain the maximum number of non-cumulated or conjugated double bonds ('wikt:mancude, mancude'). They have the general formula C''n''H''n'' (when ''n'' is an even number) or C''n''H''n''+1 (when ''n'' is an odd number). The IUPAC nomenclature, IUPAC accepts the use of 'annulene nomenclature' in naming carbocyclic ring systems with 7 or more carbon atoms, using the name '[''n'']annulene' for the mancude hydrocarbon with ''n'' carbon atoms in its ring, though in certain contexts (e.g., discussions of aromaticity for different ring sizes), smaller rings (''n'' = 3 to 6) can also be informally referred to as annulenes. Using this form of nomenclature 1,3,5,7-cyclooctatetraene is [8]annulene and benzene is [6]annulene (and occasionally referred to as just 'annulene'). The discovery that [18]annulene possesses a number of key properties associated with other aromatic molecules was an important development in the understanding ...
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