annulene chebi_ontology CHEBI:33662 A mancude monocyclic hydrocarbon without side chains of the general formula C<small>_<em>n</em></small>H<small>_<em>n</em></small> (<em>n</em> is an even number) or C<small>_<em>n</em></small>H<small>_<em>n</em>+1</small> (<em>n</em> is an odd number). In systematic nomenclature an annulene with seven or more carbon atoms may be named [<em>n</em>]annulene, where <em>n</em> is the number of carbon atoms. monocyclic hydrocarbon