Concept

Cyclododecahexaene

Résumé
Cyclododecahexaene or [12]annulene (C12H12) is a member of the series of annulenes with some interest in organic chemistry with regard to the study of aromaticity. Cyclododecahexaene is non-aromatic due to the lack of planarity of the structure. On the other hand the dianion with 14 electrons is a Hückel aromat and more stable. According to in silico experiments the tri-trans isomer is expected to be the most stable, followed by the 1,7-ditrans and the all cis-isomers (+1 kcal/mol) and by the 1,5-ditrans isomer (+5 kcal/mol). The first [12]annulene with sym-tri-trans configuration was synthesized in 1970 from a tricyclic precursor by photolysis at low temperatures. On heating the compound rearranges to a bicyclic [6.4.0] isomer. Reducing the compound at low temperatures allowed analysis of the dianion by proton NMR with the inner protons resonating at -4.5 ppm relative to TMS, evidence of an aromatic diamagnetic ring current. : In one study the 1,7-ditrans isomer is gene
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