Annulene

Annulenes are fully conjugated monocyclic hydrocarbons of the general formula (CH ) n, where n is the size of the ring denotes and is prefixed with the short name of the annulenes in square brackets. 1,3 - cyclobutadiene would demnachAnnulen. This simplified nomenclature for determining monocyclic hydrocarbons was introduced by Franz Sondheimer after the first successful synthesis einesAnnulens ( 1,3,5,7,9,11,13,15,17 - Cyclooctadecanonaen ). For pure hydrocarbon compounds the size of the ring is also suitable as a quantitative indication of the π - electrons. This is according to the Hückel rule is one of the key criteria for assessing the aromaticity of conjugated Ringsystems.Annulen However, although complying with the rule, not aromatic because of steric hindrance of the formation of a planar geometry is prevented by this connection also exist several cis- trans -isomer.