Tetrahedrane

Tetrahedrane is certainly to be found amongst any collection of consummately strained polycyclic hydrocarbons. While the 2-dimensional cyclopropane is composed of three carbons and a single strained 3-membered ring, the 3-dimensional tetrahedrane is made of four carbons and a number of strained cyclopropanes as faces. As befits relative availability and seemingly stability as well, there is yet only one thermochemically characterized tetrahedrane, the tetra-t-butyl derivative [29], for which both condensed and gas phase enthalpies of formation are available [30], 

From this approach, the predicted value of the enthalpy of formation of gaseous tetrahedrane is ca. 402 kJ mol1. 

The (non-combustion calorimetrically) experimentally determined enthalpies of formation for benzvalene [31], semibullvalene [32], and triquinacene [33] are 363, 308, and 224 kJ mol1 respectively. Assuming linear dependence of enthalpy of formation on any of these counts (r2 = 0.98), we derive a value for the enthalpy of formation of tetrahedrane of 437 kJ mol1. The equivalent non-statistical derivation is to assume thermoneutrality for the reaction 

The necessary enthalpy of formation of cubane [34] is 622 kJ mol-1, and that of prismane [35] is taken as ca. 570 kJ mol1. Linear extrapolation gives the enthalpy of formation of tetrahedrane as ca. 518 kJ mol1. Alternatively, in the absence of a measured enthalpy of formation data for prismane, we assert thermoneutrality for the formal reaction 

The final approach discussed here for estimating the enthalpy of formation of tetrahedrane is to assume the reaction 

Tetrahedrane, 1, C4H4 or (CH)4 is interesting for at least four reasons  

Levjars, Modeling Marvels, DOl 10.1007/978-l-4020-6973-4 6, Springer Science+Business Media B.V. 2008 

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THE cvcLOBUTADENE-TETRAHEDRANE SYSTEM. A related reaction is the photoisomerization of cyclobutadiene (CBD). It was found that unsubstituted CBD does not react in an argon matrix upon irradiation, while the tri-butyl substituted derivative forms the corresponding tetrahedrane [86,87]. These results may be understood on the basis of a conical intersection enclosed by the loop shown in Figure 37. The analogy with the butadiene loop (Fig. 13) is obvious. The two CBDs and the biradical shown in the figure are the three anchors in this system. With small substituents, the two lobes containing the lone electrons can be far... 

The irradiation of tetra-/-butylcyclopentadienone with 254 nm light at 77 K produced a tricyclopentanone which, upon extended irradiation, lost carbon monoxide. Tetra-f-butyltetrahedrane was formed. This derivative of the second fundamental hydrocarbon of molecular formula (CH), namely tetrahedrane, is stable at room temperature and could be isolated after chromatography on silica gel in crystalline form (G. Maier, 1978). 

Taxus baccata 656 Taxus brevifolia 655 Tebbe reagent 703 telomerization 354 ff. a-terpineol 5 tertiary radicals 409, 413 tether, disposable 664 tetrahedrane 12... 

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. 

During all these studies on cyclobutadienes and tetrahedranes formed via carbenes as transient species we wondered whether matrix isolation IR spectroscopy might be a good tool for the direct observation of cyclopropenylidene (2) and trimethylenemethane (3). This is indeed the case. 

FIGURE 5.7 Momentum density isosurfaces (in a.u.) of cyclopropane and (a) momentum density of tetrahedrane along the p. axis. Parts b, c, and d show the variation of the density for the same axis for a single, two, and three CH2 insertions, respectively. 

Figure 25 Synthesis and structures of supersilyl-substituted gallanyls 396 and 400, gallanide 398 and tetrahedrane 401.

Tetrahedron. Sn2Bi22- and Pb2Sb22 have (2)(2) + (2)(3) + 2 = 12 skeletal electrons for tetrahedra analogous to P4 and organic C4R4 tetrahedrane derivatives (see Section 1.1.3.4). 

In addition, R 4Si4 (R = Dis2MeSi with Dis = CH(SiMe3)2 has been synthesized by reaction of R Br2Si-SiBr2R and NaR in THF [17]. The tetrahedrane (Si-Si,.rldo/... 

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