Bonds to Silicon, Phosphorus, and Sulfur

Lure detennined by X-ray diffraction [118]. The twist in the a framework is approximately 60°. As in the case of traw-cyclooctene, both ends of the n bond are pyramidally distorted in such a way as to reduce the twist angle of the p orbitals to 29°. 

Copyright 2001 John Wiley Sons, Inc. ISBNs 0-471-35833-9 (Hardback) 0-471-22041-8 (Electronic) 

Orbital Interaction Theory of Organic Chemistry, Second Edition. Arvi Rank 

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Orthoboric acid forms white, needle-like crystals in which B(0H)3 units are linked together by hydrogen bonds to form infinite sheets. The ortho prefix indicates that this particular oxyacid of B(III) is formally the most fully hydrated one. This nomenclature also carries over to oxyacids of other nonmetals such as silicon, phosphorus, and sulfur. 

Elements of the second row possess d orbitals of sufficiently low energy to participate in bonding. In general, however, d orbitals are not used for a bonding, but, via hybridization, for n bonding. This hybridization increases the stability of the molecule. Hybridization is most marked in silicon, phosphorus, and sulfur. These elements are therefore polymeric in the solid state, and even less condensed states show to some extent a high chain-link number. 

The elements to the right of silicon are all non-metallic elements. They exist as relatively small molecules. Sulfur exists as Sg molecules, phosphorus as molecules and chlorine as Cl molecules. Although the covalent bonds within each molecule are strong, there are only relatively weak van der Waals forces between their molecules (see page 62). Therefore, it does not take much energy to break these weak intermolecular forces and melt the elements. At room temperature, phosphorus and sulfur are solids with low melting points and chlorine is a gas. 

Olefin synthesis starts usually from carbonyl compounds and carbanions with relatively electropositive, redox-active substituents mostly containing phosphorus, sulfur, or silicon. The carbanions add to the carbonyl group and the oxy anion attacks the oxidizable atom Y in-tramolecularly. The oxide Y—O" is then eliminated and a new C—C bond is formed. Such reactions take place because the formation of a Y—0 bond is thermodynamically favored and because Y is able to expand its coordination sphere and to raise its oxidation number. 

Element-element bonds, addition to G-G multiple bonds arsenic—selenium bonds, 10, 782 boron—boron bonds, 10, 727 boron—sulfur bonds, 10, 778 B-S and B-Ge bonds, 10, 758 chalcogen—chalcogen additions, 10, 752 germanium—germanium bonds, 10, 747 germanium-tin bonds, 10, 780 overview, 10, 725-787 phosphorus—phosphorus bonds, 10, 751 phosphorus—selenium bonds, 10, 782 phosphorus-sulfur bonds, 10, 781 Se-Si and Se-Ge bonds, 10, 779 silicon-germanium bonds, 10, 770 silicon-phosphorus bonds, 10, 780 silicon-silicon bonds, 10, 734 silicon-sulfur bonds, 10, 779 silicon-tin bonds, 10, 770 tin-boron bonds, 10, 767 tin-tin bonds, 10, 748... 

The class of phosphaalkenes with isolated P=C double bonds was first synthes ized by Becker.33 His synthetic strategy starting from trimethylsilylphosphines and acyl chlorides is still the most versatile (Protocol 3). The principle is based on the easily achievable, 1,3-silatropic migration of a silyl group bonded to phosphorus to a doubly bonded element such as nitrogen, oxygen, or sulfur. The process is favoured energetically by the construction of the P=C double bond with concomitant formation of a very stable silicon-element bond. 

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