Prismane molecules

Table 4 summarizes the structural parameters of prismane molecules (M6H6 M = C, Si, Ge, Sn) together with the calculated values for R=H. The M—M bonds within and between the three-membered rings are denoted as a and b, respectively. The calculations predicted that a is shorter than b for R = H7,8, which is in accordance with the experimental data... 

In 1982, the synthesis and properties of a new polycyclic C2oH2o hydrocarbon, dodecahedrane, was reported [21], The twenty carbon atoms of this molecule are arranged like the vertices of a regular dodecahedron. When, in the early 1960s, H. P. Schultz discussed the topology of the polyhedrane and prismane molecules (vide infra) [22], at that time it was in terms of a geometrical diversion rather than true-life chemistry. Since then it has become real chemistry. 

An interesting comparison is offered by the prismane molecule, a polycyclic hydrocarbon with formula whose carbon and hydrogen atoms are arranged in the shape of a six-atom triangular prism. The magnetic symmetry is the same as cyclopropane s D-jhiCih)- It is a valence isomer of benzene, far less stable than the archetypal aromatic molecule. A spatial ring current model for this molecule has been reported [115]. 

Butyne trimerizes in the presence of aluminum chloride to give hexamethyl Dewar-benzene (W. Schafer, 1967). Its irradiation leads not only to aromatization but also to hexa-methylprismane (D.M. Lemal, 1966). Highly substituted prlsmanes may also be obtained from the corresponding benzene derivatives by irradiation with 254 nm light. The rather stable prismane itself was synthesized via another hydrocarbon, namely benzvalene, a labile molecule (T. J. Katz, 1971, 1972). 

A preliminaiy characterization of a new iron—sulfur protein isolated from Desulfovibrio vulgaris Hildenborough was reported in 1989 124). The protein contained approximately 6 iron and 6 inorganic sulfur atoms per molecule. The FPR spectrum of the dithionite reduced protein exhibited an S = signal similar to what was found for synthetic compounds with a [6Fe-6S] core (prismane core). No other FPR signals were reported at this time, and based on the observed similarity it was suggested that this peculiar iron-sulfur protein contained a [6Fe-6S] cluster. Because it had no known function, the pro-... 

Molecules such as P4 and the polyanionic clusters such as Si4- or As2- that are discussed in Section 13.2 are representatives of electron precise closo clusters. Organic cage molecules like tetrahedrane (C4R4), prismane (C6H6), cubane (C8H8), and dodecahedrane (C20H20) also belong to this kind of cluster. 

For benzene several isomers are possible, most of them suggested in the last century as possible structures for benzene before the Kekule model was proposed and accepted. Prismane, Dewar benzene, and benzvalene (see Fig. 5) all might be formed from excited benzene molecules provided proper modes of vibration were... 

In summary, the radical cations of the benzene valence isomers show several interesting structures. Although most of their structural features can be rationalized by considering the HOMOs of the precursor molecules, some of the species show substantial changes in individual bond lengths. Accordingly, species such as the 2B2 and 2A1 Dewar benzene radical cations, the 2Bj and 2At benzvalene radical cations, or the 2Bt prismane radical cation cannot be expected to qualify as Koopmans radical cations. To date, most of the information available in this series is based on CIDNP results and ab initio calculations. It is safe to predict increasing involvement of ESR spectroscopy in this area. 

Here, we deal with clusters such as prismane, CeHe, and cubane CgHg, which can simply be described in terms of edge-localized two-center, two-electron bonds. Why, then, is it necessary to devote any space to such molecules The answer is that it was not initially clear how TSH theory can rationalize the electron counts of these molecules. Of course, this is not entirely surprising, as the Hybridization patterns used in the TSH model are not well adapted to cover this situation. However, the correct answer can be obtained without abandoning the framework developed in the preceding sections. 

The randomization of carbon and hydrogen atoms in benzene which occurs on electron impact 54) is analogous to the numerous skeletal rearrangements in the benzene series that occur upon photolysis.55,56) jiie rearrangements of the benzene molecule ion must proceed through structures that are related to known products of benzene photolysis, i.e., benz-valene, 38, prismane, 39, Dewar benzene, 40, and hexadienyne, 47. The open chain form of the benzene molecule ion, 41, has been a subject of... 

From a purely synthetic viewpoint, triazolinedione adducts have served as substrates for gaining access to numerous target molecules such as prismane, semibullvalene, bridged semibullvalenes, elassovalene, caged compounds, and azoalkanes. Indeed, the title reagent can be used not only as a chiral source, but also as an azo donor. In the synthesis of 4,5-diazatwis-4-ene, for example, (-)- nfirst step involved cycloaddition to cyclooctatetraene dibromide with formation of a separable mixture of diastereoisomers. Eventual removal of the... 

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