Silicon chemical behavior

Silicon (3), which resembles metals in its chemical behavior, generally has a valence of +4. In a few compounds it exhibits a +2 valence, and in silicides it exists as a negative ion and largely violates the normal valency rules. Silicon, carbon, germanium, tin, and lead comprise the Group 14 (IVA) elements. Silicon and carbon form the carbide, SiC (see Carbides). Silicon and germanium are isomorphous and thus mutually soluble in all proportions. Neither tin nor lead reacts with silicon. Molten silicon is immiscible in both molten tin and molten lead. 

As mentioned above the 1,1-organoboration reaction is reversible, and exchange is slow on the NMR timescale. This statement is in agreement with the chemical behavior of equilibrated mixtures of products. Thus, treatment of silicon borahomoadamantane derivative 92 with bis(trimethylstannyl)ethyne leads to the tin-containing compound 93 and liberation of bis(trimethylsilyl)ethyne (Scheme 44). With pyridine, the equilibrium is moved toward 1-boraadamantane completely due to the complexation <2001JOM(620)51>. 

The effects of silyl groups on the chemical behavior of the anion radicals generated by cathodic reduction is also noteworthy. It is well known that silyl groups stabilize a negative charge at the a position. Therefore, it seems to be reasonable to consider that the anion radicals of re-systems are stabilized by a-silyl substitution. The interaction of the half-filled re orbital of the anion radical with the empty low-lying orbital of the silicon (such as dx-pK interaction) results in partial electron donation from the re-system to the silicon atom which eventually stabilizes the anion radical. 

Mechanisms for the substitution at silicon in solution have been a subject of several reviews (7-15). Since expansion of the coordination number of silicon is a common feature, particular interest is directed to mechanisms involving intermediates or transition states with silicon having a coordination number of 5 or 6. So far, little attention has been devoted in the review literature to mechanistic pathways that do not invoke extracoordination. Knowledge of these mechanisms, however, has often become necessary for the understanding of chemical behavior of organosilicon compounds. In this article we discuss mechanistic pathways involving heterolytic cleavage... 

The differences in the chemical behavior of silicon, relative to carbon, is responsible for the elusiveness of SiR3 compounds in condensed phases. Just is it that what hampers the observation of silyl cations, although they are intrinsically thermodynamically more stable than carbenium ions ... 

It should be noted that oxygen vacancies at oxide surfaces are of major importance for the physical and chemical behavior of these systems, apart from consequences for catalytic reactivity. As examples we mention point defects at silicon dioxide [130] or the existence of color centers at MgO surfaces which are due to localized electron states at oxygen vacancy sites and have been discussed extensively in the literature [131]. 

Silicon (Si) is the second most abundant element in the earth s crust, contributing around 28%. Silicon acts as a nonmetal in its chemical behavior but its electrical and physical properties are those of a semimetal. Crystalline silicon is a gray, lustrous solid. The chemistry of silicon is dominated by compounds that contain the silicon-oxygen (Si-O) linkage. 

Summary The synthesis of the pentacoordinated silane (2-Me2NCH2C6Hi)-(CH=CH2)Si(H)2 (1) is described. A comparison of the chemical behavior of hypervalent 1 with tetravalent silicon compounds is carried out. 

Interpreting Data An unknown element has chemical behavior similar to that of silicon (Si) and lead (Pb). The unknown element has a mass greater than that of sulfur (S), but less than that of cadmium (Cd). Use the periodic table to determine the identity of the unknown element. 

Now that we are able to understand the chemical behavior of many main-group elements such as lithium, silicon, boron, and aluminum, the purpose of this book is to summarize these recent developments and show the promising future roles of complexes of these metals in modern organic synthesis. In fact, these reagents are both useful and much safer than most transition-metal compounds. 

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