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Cyclododecahexaene or annulene (C12H12) is a member of a series of annulenes with some interest in organic chemistry with regard to the study of aromaticity  These compounds are in general unstable due to their antiaromaticity and built-up of steric strain. On the other hand the di-anion with 14 electrons is a Hückel aromat and more stable.
Additional recommended knowledge
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 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 generated at low temperatures in THF by dehydrohalogenation of a hexabromocyclododecane with potassium tert-butoxide. Reduction of this compound at low temperature with cesium metal leads first to the radical anion and then to the dianion. The chemical shift for the internal protons in this compound is with +0.2 ppm much more modest than in the tri-trans isomer.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Cyclododecahexaene". A list of authors is available in Wikipedia.|