Silicon atoms, free reactions

In the cathodic regime the silicon atoms of the electrode do not participate in the chemical reaction. Therefore, an n-type or a strongly illuminated p-type silicon electrode behave like a noble metal electrode and hydrogen evolution or metal plating reactions are observed. For the case of an aqueous electrolyte free of metal ions the main reaction is electrochemical hydrogen evolution according to ... 

The kinetics of the acid catalyzed hydrolysis of ethoxysilanes has been studied. Each of the silanes that were used had a phenyl or para-substituted phenyl group attached to the silicon atom. This permitted a study of the linear free energy relationships of this reaction. The reaction is of interest because of its role in silane coupling agent chemistry, in the preparation of zinc-rich silicate coatings, in the sol-gel process and in the preparation of silicones in general. 

The reaction of MeLi in Et20 with alkyl- and aryl-substituted branched tetrasilanes proceeds by cleavage of one Si—Si bond, thus affording various trisilanes, which are lithiated at the central silicon atom (equation 26)62. The outcome of these reactions apparently is insensitive as to whether halide-free MeLi or the MeLi-LiBr complex is used62. The decrease in the reaction rate in the order R = Tip > Mes > Ph has been suggested by Fink and coworkers to reflect the relief of steric strain on converting the tetrasilane into the metalated silane626. 

Insertion, addition and abstraction reactions of free silicon atoms can lead to the formation of silylenes (equation 9)1-5. Silylene formation for reaction, spectroscopic and... 

The free iodine can readily he washed out, but CaCl2 can be removed only incompletely because all the solvents for this substance react with silicon chloride. The reaction will take place quantitatively only if the starting CaSi2 has been finely ground under inert gas or in a solvent. Grinding in air leads to partial oxidation and the reaction remains incomplete. Silicon monochloride prepared in this way is a yellow scaly product whose analysis indicates the exact 1 1 silicon to chlorine ratio. The quantity of hydrogen liberated in alkaline medium is also consistent with the three Si-Si bonds per silicon atom required for the layer structure. 

This method using grafting to one silicon atom of SC makes it possible to approach spatially two chemically different groups r and rt and obtain free radical structures of the (=Si-0-)2Si(r )(r) type. This leads to more diverse intermediates on the solid surface and allows one to study new chemical processes involving these intermediates, including intramolecular reactions between r and /y groups. The low-molecular radicals necessary for the first step of SC modification can conveniently be obtained from the saturated H-r molecules, and appropriate defects on the silica surface can be used as... 

The dissolution reaction (change in free enthalpy Ag1 ) implies the breaking of too Si-O-Si bonds ( per silicon atom) and the formation of four silanol groups (Kith disappearance of tno Hater molecules). On the other hand the polymerization reaction (change in free enthalpy AG) corresponds to the formation of a Si-0-Si bond (and a Hater molecule) and to the disappearance of tno silanol groups. It can thus be nritten to a first approximation ... 

At higher temperatures the methylchlorosilanes themselves appear to react with aluminum, furnishing methyl groups for the further alkylation of some molecules at the expense of others which are reduced to free silicon. This actually is a form of disproportionation, in which organic groups are stripped from some silicon atoms and attached to others. In this and the similar reactions zinc or aluminum acts as halogen acceptor. 

During the past eight years, we have studied the reactions of thermally generated silicon atoms with a variety of low-molecular-weight reactants in an argon matrix. The reaction products were identified by means of IR and UV/Vis spectroscopy aided by comparison with calculated spectra. The method turned out to be very versatile and successful [1]. The selected substrates were mainly molecules with isolated, conjugated or aromatic n bonds, and compounds containing a bonds and at the same time free electron pairs. 

Surface Reaction Kinetics-Based Models. The basic consideration in reaction kinetics models is that the reaction rate is determined by the lattice strueture on the surface. The difference in the lattice structures of various crystal planes gives rise to differences in surface bond density, electron density, surface free energy, and so on, which then determine the dissolution rate of the surface silicon atoms. All etching... 

ESR experiments also indicate that a substantial concentration of free radicals is present in the solids, which corroborates the participation of radical species during the decomposition. A variety of radical combination and abstraction reactions are possible at high temperature and can account for the various hydrocarbons and silane products observed. In general, hydrogen atom as well as carbon or silicon atom centered radicals coid be created (c.f. Scheme 17). 

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