Beta silicon effect

The beta silicon effect , referring to the strong stabilization of carbocations -substituted with silicon, is another well-known manifestation of hyperconjugation. The C-Si empty orbital on a cationic center, very significant delocalization is observed. Finally, an important feature in the conformational analysis of alkenes is the tendency for allylic sp centers to prefer to eclipse the C=C double bond (Scheme I) (see Conformational Analysis I Conformational Analysis 2 and Conformational Analysis 3). This preference, typically on the order of 2 kcal moI , is ascribed to improved hypercon-jugative interactions of the non-eclipsing C-H bonds with the jr orbital of the alkene for this conformation. 

The promising electronic properties of beta-silicon carbide are compared to those of other semiconductor materials in Table 8.3 of Ch. 8. A major advantage of this material is its high-temperature potential (>1000"C) which far surpasses that of other semiconductors. Beta-SiC should also be more effective than silicon or gallium arsenide particularly in microwave and millimeter-wave devices and in high-voltage power devices. The development of SiC as a semiconductor is still in the laboratory state. 

Chemistry Ti-6246 is a solid-solution-strengthened alloy end Density that responds to heat treatment as a resiilt of the beta-stabilizing effect of its 6% molybdenum content. Silicon additions (0.08 wt%) improve creep... 

This computation is also referred to as calculating the zinc equivalent of the alloy. The increase in strength in this alloy series is caused by increased amounts of beta phase in the stmcture. The silicon brasses show similar hardening effects accompanying a second phase. Typical mechanical properties and electrical conductivity for various cast alloys are shown in Table 2. 

The 10 beta effect of mercury is larger than that of silicon and comparable to that of germanium. Interestingly, hyperconjugative assistance with mercnry increases with the nucleophilicity of the solvent, suggesting that coordination of solvent with mercnry in the transition state increases polarizability and nucleophilicity of... 

The main feature of the Meerwein-Ponndorf-Verley reaction pathway involves the coordination of both reactants to the Lewis-acid metal eentre and hydride transfer from the alcohol to the earbonyl group. Aluminium or titanium alkoxides are usually effective homogeneous catalysts. With tin-Beta catalyst, cyclohexanone reduction with 2-butanol led selectively to cyclohexanol at 100 °C. Ketone conversion was >95%, whereas silicon-Beta, Sn02/Si02 and SnCl4 -5H20 were inaetive under the same experimental conditions. Therefore, the activity is likely due to tetrahedral tin in the zeolite framework, and not to extra-framework tin or to leached tin. ... 

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