Tetracarbon structures

In the first group of syntheses, three carbon substrates (e.g., d- and L-glyceraldehyde d- and L-lactaldehyde) and tetracarbon, (e.g., L-threose) are often elongated by addition reaction to the carbonyl group—Wittig or aldol reactions (Scheme 1)—and the products obtained are subsequently converted into required structures. 

The structure of tetracarbon monofluoride (C4F) has been discussed by Riidorff Riidorff (1947 6) and Riidorff (1959). While it cannot be unequivocally demonstrated from their X-ray powder diffraction data, they proposed that in C4F the carbon atom sheets were flat and that the fluorine atoms made close ca. 1.4 Af) contacts to the carbons. Their finding ofhigh electrical conductivity for C4Fj, j(HF)4 also supported their notion that the carbon atom sheets were planar. Recent work in these laboratories (Mallouk Bartlett 1983 Mallouk 1983) has established that chemical fluorination of graphite, to compositions C4.Fj, 5(HF),5, x > 2.3, may... 

Structural studies made up to the present lead to the generalization that in a graphite compoimd all C—C distances in the carbon layers, apart from lattice imperfections, are the same and that the layers are either plane or puckered, even when some of the carbon atoms have a different type of bonding. In carbon monofluoride and tetracarbon monofluoride the two possible structures for the carbon layers are realized. 

The electron band structure of the Tetracarbon films was found to be quite different from that of diamond, graphite and all other known forms of carbon and was consistent with linear chains as a basic element of the atomic structure this was clearly shown by electron spectroscopy measurements with electron excitations [1,2]. In the present work this fact was... 

Thus, inter-atomic distances and the atomic state in Tetracarbon are fundamentally different from all the known forms of carbon. The differences between clear and hard diamond on the one hand, and soft and black graphite on the other hand, illustrate the differences among Tetracarbon and other forms of carbon. The distance between the neighboring sp -carbon atoms within the Tetracarbon chain is about 1.3 A, whereas the distance between the carbon chains is 4.80-5.03 A. It is interesting to note that in some respects Tetracarbon is similar to tubulenes, as it can be considered as tubulene in the limit when the diameter of the tube approaches the diameter of carbon atom. Nevertheless, in Tetracarbon the hybridization state of carbon atoms changes from sp to sp. It is basically a new purely one-dimensional sp -carbon modification with one-dimensional electron band structure, whereas tubulene is a quasi-one-dimensional material in which the number of one-dimensional electron bands increases with increasing tubulene diameter. Tetracarbon and tubulene are also similar in that the carbon chains in Tetracarbon are oriented normally to the surface of the film, similar to the orientation in tubulene. 

The sp modification carbyne briefly described below is characterized by a different intrinsic structure and can be obtained only in the form of very small particles. Another analogous example is the sp molecular crystals which are composed of short sp -carbon chains with organic caps on the ends of the chains, which prevents them from collapsing into the amorphous state [28]. These crystals are not composed of pure sp -hybridized carbon and are stacked into a cross-linked crystal structure, which is easily dissolved in many organic solvents and is completely different from Tetracarbon . 

Tetracarbon dioxide is an unstable oxide of carbon with the following molecular structure ... 

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