Computational cumulenes

Aside from fuUerene research, carbon clusters have always attracted much interest among scientists. " Linear cumulene-like Ce (Pooh) 132 is well known from computational studies as well as experimentally. " Cyclic Cg, which will be considered as the extreme case of a dehydrobenzene here, has a long and varied history. " In particular, two cyclic isomers possessing D h and Dg/, symmetry (133 and 134) have been discussed. " According to the most recent calculations, 133 ( Aj) is lowest in energy 134 ( Ai ) and 132 ( S )) being less stable by 8 and 10 kcal/mol, respec-tively. 42-... 

While computations involving [96]+ did not converge, the calculated structure of the dication is in good agreement with the experimentally observed cumulenic form. In terms of the simple Hfickel model, double oxidation of 96 is consistent with the depopulation of the higher lying 4ji level. In the case of the iron complex 107, the first two oxidation processes resulted in an increase in the acetylenic character of the carbon chain and... 

A detailed computational study of the bonding in the zirconocene cyclopentyne complex suggests that the metallacyclopentyne depiction does not adequately describe the electronic structure of the complexes.152 The structure is best represented as a hybrid intermediate between the cumulene complex and the metallacyclopentyne... 

Computational studies have compared substituent effects on the stability of ketenes, allenes, diazomethanes, diazirines, and cyclopropenes. Ketenes belong to the first generation of reactive intermediates along with carbocations, carbanions, radicals, and carbenes, and are intensively studied members of the cumulene family, with many useful synthetic applications. Ketenes were first recognized in 1905, when diphenylketene, a stable and isolable example, was obtained from the dehalogenation of the a-bromodiphenylacetyl bromide (Scheme 7.37). The most characteristic reaction of ketene is cycloaddition, as in the formation of p-laclams. 

---