Effect of silicon compounds

Table 8a. Effects of silicon compounds 44 and 46-57 in the electroshock test6...

Figure 7. Effect of silicon compound structure on the Si02 deposition in irradiated PMANI(B) film at 30 °C. Silicon compound ( ) MTMOS, (O) TMOS, ( ) MTEOS, ( ) TEOS, (a) TPOS. E q)osure dose 62 naJ/cm. Polymer wei t 2 X 10 g. Surface area 1.9 ca. Relative humidity 95%.

Although prior research has established the interference effect of aluminum, previous in-house studies on the atomic absorption analysis of silicate materials indicated that silicon may also have an interference effect. This interference is probably caused by compound formation in the flame. The effect of silicon on the determination of all of the elements... 

The electronic effects of an R3 S i group can be divided into four components (i) inductive effects, (ii) field effects, (iii) (p-d) jr bonding and (iv) hyperconjugative effects. The total electronic effect of an R3 S i group in a molecule or intermediate will be a combination of these effects, and much effort has been made in the last ten years to quantify the contributions of the various effects to certain properties of silicon compounds, particularly as regards the importance of (p-d) jr bonding and hyperconjugative effects. 

In addition to the stabilization of /1-carbocations, the /1-effect of silicon can also be observed in the ground states of neutral molecules. Lambert and Singer58 studied compounds of the type 42 where hyperconjugation should be enhanced by increasing the electron-accepting properties of the substituent X (MeO < Me < H < CN). o-tt overlap in this system gives the resonance structure 43 shown in equation 19. 

The first report of a distinct effect of silicon on a neighbouring carbenium ion was published as early as 1946. Sommer, Whitmore and coworkers34 35 reported that under conditions of basic hydrolysis, (l-chloroethyl)trichlorosilane 58 and (1-chloropropyl)trichlorosilane 59 failed to give cleavage of the a-C—Cl bond, while under the same conditions the analogous 2-chloroethyl 60 and 2-chloropropyl compounds 61 hydrolyse rapidly. 

Substitution of a silicon atom for another atom in a biologically active compound should provide clues to structure-activity relationships. The structural and electronic effects of silicon substitution are, to a reasonable extent, predictable. For example, substitution of a silicon atom for a carbon atom places a slightly larger, more electropositive, atom in the... 

The y-effect of silicon is implicated in the silicon-promoted Nef reaction.133 The Nef reaction of 5-nitrobicyclo[2.2.1]hept-2-ene 156 yields none of the expected ketone 157 (Scheme 24), whereas Nef reaction of the corresponding trimethylsilyl-substituted nitro compound 158 results in the formation of high yields of the ketone 159. The silicon is believed to promote the breakdown of the hydrated intermediate 160 by stabilizing the y-carbenium ion 161 (Scheme 25). 

Tetraethoxysilane is the main raw stock in the production of valuable silicone products, e.g. heat-resistant and insulating varnishes, or oli-goethylsiloxane liquids. The most important chemical property of tetraethoxysilane is its ability to replace the ethoxyl group with an organic radical under the effect of metalorganic compounds, i.e. to form substituted ethers of orthosilicon acid, which are the raw stock in the production of the silicone products mentioned above. 

Cf. the Chemistry Award Lecture of the Academy of Science in Gottingen 1969 by H. Bock, The Perturbation of n Systems as a Molecular Probe of Substituent Effects , Jahrb. Akad. Wiss. Gottingen, 1969, pp. 13-25. For a summary of silicon compounds investigated see Ref. 40. 

Organic derivatives of silicon compounds particularly those involving Si-O-C and Si-N( )-C bonds are of great synthetic importance as intermediates which, when suitably reacted (usually via solvolysis), lead to the desired organic fine chemicals [ 146a]. These classes of compounds may be effectively synthe-... 

Whereas numerous reactivity studies have been reported for a wide variety of silicon compounds and catalysts, caution is advised when comparing rate data and accepting mechanistic proposals. The uncertainty arises from the lack of uniformity of reaction conditions, especially regarding the presence of water and oxygen, both of which have significant effects on rate and product distribution. 

The exact mechanism responsible for the nephrotoxic effect of silicon remains to be elucidated although membrane damage possibly related to oxidant generation [89] or inhibition of superoxide dismutase activity [91] might be rational explanations. Based on reports on lung toxicity related to the chemical, morphological and surface characteristics of the various sihcon compounds, it is not known yet to which extent these exhibit direct toxic effects at the level of the kidney [90,92]. 

In this sub-section it is not intended to cover the thermochemical aspects of all substituted silicenium ions described in the literature. Rather, we focus on some selected systems which deem to serve as good representatives and the discussion of which may provide an understanding of the substituent effects operative. Some aspects will also be described later in conjunction with ion/molecule reactions of silicon compounds. 

Silicone Treatment of Surface of Film. Because of the improvement in desalinization obtained by treating the early cellophane membranes with silicone compounds, the effect of silicone treatment on the Schleicher and Schuell membranes was investigated. No improvement in desalinization resulted. 

---