Lewis silicon

H.S. Gandhi, W.B. Williamson, R.L. Goss, L.A. Mareotty and D. Lewis, "Silicon Contamination of Automotive Catalysts," Society of Automotive Engineers Paper No. 860565 (February, 1986). 

R. N. Meals and F. M. Lewis, Silicones, Reinhold Publishing Corp., New York, 1959. 

Figure B3.3.14. Template molecule in a zeolite cage. The CFIA stmcture (periodic in the calculation but only a fragment shown here) is drawn by omitting the oxygens which are positioned approximately halfway along the lines shown coimecting the tetrahedral silicon atoms. The molecule shown is 4-piperidinopiperidine, which was generated from the dicyclohexane motif suggested by computer. Thanks are due to D W Lewis and C R A Catlow for this figure. For fiirther details see [225].

Epoxides are regio- and stereoselectively transformed into fluorohydrins by silicon tetrafluoride m the presence of a Lewis base, such as diisopropyleth-ylamme and, m certain instances, water or tetrabutylammonium fluoride The reactions proceed under very mild conditions (0 to 20 C in 1,2-diohloroethane or diethyl ether) and are highly chemoselective alkenes, ethers, long-chain internal oxiranes, and carbon-silicon bonds remain intact The stereochemical outcome of the epoxide ring opening with silicon tetrafluoride depends on an additive used, without addition of water or a quaternary ammonium fluoride, as fluorohydrins are formed, whereas m the presence of these additives, only anti opening leading to trans isomers is observed [17, 18] (Table 2)... 

Silicon compounds can also act as Lewis acids, whereas carbon compounds typically cannot. Because a silicon atom is bigger than a carbon atom and can expand its valence shell by using its d-orbitals, it can accommodate the lone pair of an attacking Lewis base. A carbon atom is smaller and has no available d-orbitals so in general it cannot act as a Lewis acid. An exception to this behavior is when the carbon atom has multiple bonds, because then a Tt-bond can give... 

Carbon is the only member of Group 14/IV that commonly forms multiple bonds with itself singly bonded silicon atoms can act as Lewis acids because a silicon atom can expand its valence shell. 

Silicon reacts directly with chlorine to form silicon tetrachloride, SiCl4 (this reaction was introduced in Section 14.17, as one step in the purification of silicon). This compound differs strikingly from CC14 in that it reacts readily with water as a Lewis acid, accepting a lone pair of electrons from H20 ... 

Carbon forms ionic carbides with the metals of Groups 1 and 2, covalent carbides with nonmetals, and interstitial carbides with d-block metals. Silicon compounds are more reactive than carbon compounds. They can act as Lewis acids. 

Price C, Waters MGJ, Williams DW, Lewis MAO, and Stickler D. Surface modification of an experimental silicone rubber aimed at reducing initial candidal adhesion. J Biomed Met Res, 2002, 63, 122-128. 

The reactivities of alkenylsilanes in the presence of a Lewis acid vary depending upon the nature of substituents on silicon as shown in Table 1. 

It is well known in the literature that aluminum chloride, a strong Lewis acid, is a very effective catalyst in Friedel-Crafts alkylations with silicon... 

These compounds form an interesting contrast to the Lewis base adducts of silyl-metal carbonyls (Section II,C,4), where silicon is thought to be present in a cation. 

All these silicon reagents which activate metal surfaces are also Lewis acids, which can also contribute as such to the acceleration of any of the subsequently discussed reactions, because of their inherent Lewis acid properties. 

These TMS-carbamate-mediated NCA polymerizations resemble to some extent the group-transfer polymerization (GTP) of acrylic monomers initiated by organo-silicon compounds [40]. Unlike GTPs that typically require Lewis acid activators or nucelophilic catalysts to facilitate the polymerization [41], TMS-carbamate-mediated NCA polymerizations do not appear to require any additional catalysts or activators. However, it is still unclear whether the TMS transfer proceeds through an anionic process as in GTP [41] or through a concerted process as illustrated in Scheme 14. 

These three frameworks and the framework for glycine in Figure 9 illustrate an important point about Lewis structures. Although Lewis structures show how atoms are connected to one another, a Lewis structure is not intended to show the actual shape of a molecule. Silicon tetrachloride is not flat and square, SO2 is not linear, and the fluorine atoms in CIF3 are not all equivalent. We describe how to use Lewis structures to determine the shapes of molecules later in this chapter. 

C09-0079. Silicon forms a tetramethyl compound with the formula (0113)4 Si Determine the Lewis structure, determine the shape about each inner atom, and draw a ball-and-stick model of the compound. 

A good example is B (0113)3 which uses a vacant 2 p orbital to form an adduct with ammonia. The elements in the p block beyond the second row of the periodic table have empty valence d orbitals that allow them to act as Lewis acids. The silicon atom in Sip4 is an example. 

Bocarsly AB, Bookbinder DS, Dominey RN, Lewis NS, Wrighton MS (1980) Photoreduction at illuminated p-type semiconducting silicon photoelectrodes. Evidence for Fermi level pinning. J Am Chem Soc 102 3683-3688... 

Dominey RN, Lewis NS, Bruce JA, Bookbinder DC, Wrighton MS (1982) Improvement of photoelectrochemical hydrogen generation by surface modification of p-type silicon semiconductor photo-cathodes. J Am Chem Soc 104 467 82... 

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