Annulenes cyclobutadiene benzene cyclooctatetraene cyclodecapentaene [4]annulene [6]annulene [8]annulene [10]annulene Copyright 2010 Pearson Prentice Hall,Inc. Annulenes are hydrocarbons with alternating single and double bonds. Benzene is a six-membered annulene,so it can be named [6]-annulene.Cylobutadiene is [4]-annulene, cyclooctatetraene is [8]-annulene. Chapter 16 9Chapter 16 9 Annulenes • Annulenes are hydrocarbons with alternating single and double bonds. • Benzene is a six-membered annulene, so it can be named [6]-annulene. Cylobutadiene is [4]-annulene, cyclooctatetraene is [8]-annulene