Tetrahedron Theory

The second popular explanation of fire is the tetrahedron theory which is illustrated in Figure 1. This theory encompasses the three concepts in the fire triangle theory but adds a fourth side to the triangle, making it a pyramid, or tetrahedron this fourth side is called the chain reaction of burning. This theory states that when energy is applied to a fuel like a hydrocarbon, some of the carbon-to-carbon bonds break, leaving an unpaired electron attached to one of the... 

A vexing puzzle m the early days of valence bond theory concerned the fact that methane is CH4 and that the four bonds to carbon are directed toward the corners of a tetrahedron Valence bond theory is based on the overlap of half filled orbitals of the connected atoms but with an electron configuration of s 2s 2p 2py carbon has only two half filled orbitals (Figure 2 8a) How can it have bonds to four hydrogens ... 

A most important early addition to organic structure theory was made by the first Nobel Laureate in Chemistry, van t Hoff, who in 1874 recognized that the optical activity of carbon compounds can be explained by the postulate that the four valence bonds of the carbon atom are directed in space toward the comers of a tetrahedron. 

The structure theory of inorganic chemistry may be said to have been bom only fifty years ago, when Werner, Nobel Laureate in Chemistry in 1913, found that the chemical composition and properties of complex inorganic substances could be explained by assuming that metal atoms often coordinate about themselves a number of atoms different from their valence, usually four atoms at the comers either of a tetrahedron or of a square coplanar with the central atom, or six atoms at the comers of an octahedron. His ideas about the geometry of inorganic complexes were completely verified twenty years later, through the application of the technique of x-ray diffraction. 

For reviews of sulfur-containing carbanions, see Oae, S. Uchida, Y. in Patai Rappoport Stirling The Chemistry ofSulphones and Sulphoxides, Wiley NY, 1988, p. 583 Wolfe, S. in Bemardi Csizmadia Mangini Organic Sulfur Chemistry Elsevier, NY, 1985, p. 133 Block, E. Reactions ofOrganosulfur Compounds Academic Press NY, 1978, p. 42 Durst, T. Viau, R. Intra-Sci. Chem. Rep., 1973, 7 (3), 63. For a review of selenium-stabilized carbanions, see Reich, H.J. in Liotta Organoselenium Chemistry Wiley NY, 1987, p. 243. For support for this theory, see Wolfe, S. LaJohn, L.A. Bemardi, F Mangini, A. Tonachini, G. Tetrahedron Lett., 1983, 24, 3789 Wolfe, S. Stolow, A. LaJohn, L.A. Tetrahedron Lett., 1983, 24, 4071. 

In theory, the chiral center can be anywhere in the molecule, but in practice, reasonable diastereoselectivity is most often achieved when it is in the a position. For examples of high diastereoselectivity when the chiral center is further away, especially in reduction of P-hydroxy ketones, see Narasaka, K. Pai, F. Tetrahedron, 1984, 40, 2233 Hassine, B.B. Gorsane, M. Pecher, J. Martin, R.H. Bull. Soc. Chim. Belg., 1985, 94, 597 Bloch, R. Gilbert, L. Girard, C. Tetrahedron Lett., 1988, 53, 1021 Evans, D.A. Chapman, K.T. Carreira, E.M. J. Am. Chem. Soc., 1988, 110, 3560. 

The method by which this is done might ultimately be used to make a direct molecular theory for the forces on the elementary stress tetrahedron. 

Dewar, M. J. S. Angew. Chem., in press Tetrahedron Suppl. 8 (1), 75 (1966) The Molecular Orbital Theory of Organic Chemistry , McGraw-Hill Book Co. Inc., New York, N.Y. (1969). 

Rocke suggests that, like the atomic theory, the benzene theory was both extremely popularbecause it was successfulawd disbelieved in realist terms. 52 In both cases, and in the case of the carbon tetrahedron, there were two compelling problems that deterred most chemists from believing they had a real, probably true theory. 

But it was not really until 1931, when Slater and Pauling independently developed methods to explain directed chemical valence by orbital orientation that it can truly be said that a chemical quantum mechanics, rather than an application of quantum mechanics to chemistry, had been created. In a study of Slater, S. S. Schweber notes the distinction between the Heitler-London-Pauling-Slater theory and the Heitler-London theory. Heitler and London successfully explained the electron-valence pair on the basis of the Goudsmit-Uhlenbeck theory of spin. Slater and Pauling explained the carbon tetrahedron. This second explanation distinguishes quantum chemistry from quantum physics.2... 

Practitioners of quantum chemistry employed both the visual imagery of nineteenth-century theoretical chemists like Kekule and Crum Brown and the abstract symbolism of twentieth-century mathematical physicists like Dirac and Schrodinger. Pauling s Nature of the Chemical Bond abounded in pictures of hexagons, tetrahedrons, spheres, and dumbbells. Mulliken s 1948 memoir on the theory of molecular orbitals included a list of 120 entries for symbols and words having exact definitions and usages in the new mathematical language of quantum chemistry. 

Kauzmann, W., Clough, F. B., and Tobias, I. (1961) The principle of pairwise interactions as a basis for an empirical theory of optical rotatory power. Tetrahedron 13, 57-105. 

Consider one beautifully symmetrical shape predicted by VSEPR theory the tetrahedron. Four equivalent pairs of electrons in the valence shell of an atom should distribute themselves into such a shape, with equal angles and an equal distance between each pair. But what sort of atom has four equivalent electron pairs in its valence shell Aren t valence electrons distributed between different kinds of orbitals, like s and p orbitals (We introduce these orbitals in Chapter 4.)... 

The single 2s orbital combines with the three 2p orbitals to create four identical sp hybrid orbitals. The fact that each sp orbital is identical is important because VSEPR theory can now explain the symmetrical shape of methane the tetrahedron. 

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