Double aromaticity

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Aromaticity/antiaromaticity in cluster systems has certain peculiarities when compared with organic compounds. The striking feature of chemical bonding in cluster systems is the multifold nature of aromaticity, antiaromaticity, and conflicting aromaticity [3-10]. Double aromaticity (the simultaneous presence of [Pg.439]

Scheme 3.2-16. Double aromatic prototypes 32B, 33B and 34B with a- and re-aromaticity according to computations, carbenes 32A, 33A and 34A are strongly stabilized by adjacent B-B moieties. Derivatives of 12B, isoelectronic with 34B, are known experimentally [22, 44],...

Most organics with double aromatic rings show maximum adsorption on goethite at low pH. The exceptions are catchecol and dihydroxynapthalene, the adsorption of both of which rises as the pH rises from 3 to 8. Under alkaline conditions, both organics form strong surface complexes which appear to involve hydrogen bonding. 

Free bonds (FB) the bonds may connect to other substructure fragments (a free bond type can be single, double, aromatic, etc.)... 

Ogawa, Y., Ueno, T., Karikomi, M., Seki, K., Haga, K., Uyehara, T. Synthesis of 2-acetoxy[5]helicene by sequential double aromatic oxy-Cope rearrangement. Tetrahedron Lett. 2002, 43, 7827-7829. 

In 2006, the synthesis of unsymmetrical biaryls from simple arenes was achieved successfully in a catalytic system of Pd(OAc)2/TFA/K2S2Og by tuning the concentrations of arenes and TFA, reported by Lu and coworkers (Scheme 15) [61]. Although the yield of cross-coupling reaction is not practical (11-50% based on the limiting arene), it provides valuable information on the Pd-catalyzed crosscoupling reaction via double aromatic C-H activation. 

Su, X, L Liu and H Shen (1997). Studies on the fuluorimetric molecular recognition of Schiff bases containing double aromatic guests with water soluble j8-cyclodextrin cross-linking polymer. Chemical Journal of Chinese Universities, 18(8), 1275-1280 (in Chinese). 

Small and medium-size boron clusters are excellent examples where double aromaticity, double antiaromaticity, and conflicting aromaticity were shown to be able to explain their structure, stabiHty, and other molecular properties [19, 109, 110]. The following chemical bonding model was proposed for planar or quasi-planar boron clusters aU peripheral boron atoms form 2c-2e a-bonds, while the atoms inside of the peripheral ring are bound to each other and to... 

Figure 8.30 Double aromaticity in p-benzyne (through-bond) and the CJd cation (through-space).

In the course of our study on the interaction of [(NN)PtMc2] (NN = 2,3-bis(2,6-dichlorophenylimino)butane) with copper(I) or silver(I) triflates in benzene [24], we observed a double aromatic C-H activation process yielding moderate yields of [(NN)PtPh2] (Scheme 21). We proposed the mechanism depicted in Scheme 22, which involves the initial one-electron oxidatiOTi of [(NN)PtMe2] by the coinage metal, on the basis of the following considerations ... 

Another family of aromatic/antiaromatic three-membered rings of metal atoms concerns the 13 group elements (Al, Ga, In, and Tl). Kuznetsov and Boldyrev [88] reported theoretical evidence of double (a -i- jt) aromaticity in [c-Xs]" (X = B, Al, Ga) species. The [c-Xj]" clusters should be considered as earlier electron-deficient double aromatic systems, because their k-MOs are occupied earlier than in... 

The finding of the double aromaticity in Hg establishes a solid bridge between our gas-phase studies of multiply aromatic clusters and bulk materials containing such species. 

Chandrasekhar J, Jemmis ED, Schleyer PVR (1979) Double aromaticity aromaticity in orthogonal planes. The 3,5-dehydrophenyl cation. Tetrahedron Lett 39 3707-3710... 

Martin-Santamaria S, Rzepa HS (2000) Double aromaticity and anti-momaticity in small carbon rings. Chem Commun 16 1503-1504... 

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