Silicon-phenyl groups determination

In this paper detailed methods for the determination of placement and assay of silicon hydride (Si-H), silicon hydroxide (Si-OH) and silicon phenyl (Si-0) functional groups in molecular weight components of silicones of the Sylgard (Dow-Corning Co.) type will be described. The methods are illustrated with the analysis of Sylgard addition prepolymers and of model polydimethylsiloxanes (PDMS). 

Another aspect of stability of the unsaturated systems concerns the n-bond strength of the double bonded fourth group elements, the experimental determination of which certainly represents problems. Nevertheless, from n-bond migration processes some insights may be derived about the relative stability of these n-bonds as a function of the double bond substituents. In this connection, I turn first to the question Are SiC-n-bonds stabilized by mesomeric effects of silicon bonded phenyl groups ... 

A similar reaction system was used for determining alkyl groups bonded to a silicon atom [214, 215]. In this instance reaction with concentrated sulphuric acid was carried out in the presence of a vanadium catalyst, as a result of which alkyl groups were split off in the form of the corresponding hydrocarbons. Quantitative determination of ethyl and phenyl groups is also possible by their thermal cleavage from a silicon atom with the formation of ethane and benzene [216]. 

The ultraviolet spectrum of hexaphenyiditin has been determined (92), and it is proposed that there is intense interaction of phenyl groups on opposite tin atoms. The phenomenon, which occurs with analogous compounds of Si, Ge, and Pb, has been attributed in the case of silicon (119) to an excitation involving the silicon-silicon bond. The same explanation is applicable in the case of the tin-tin bond (262a). Ultraviolet spectra of hexaethylditin (250) and octadecaethylcyclononatin (188) have been reported, but without extinction coefficients. The spectra of the per-phenylated cyclostannanes have also been discussed (194a). The ultraviolet... 

This disilaborane was an unexpected co-product in the synthesis of decaborane-alkylamine polymers. The Si2Bio cluster core consists of a distorted icosahedron in which the two silicon atoms occupy adjacent positions. The Si-Si interatomic distance is 2.308(2) A, which is slightly less than the Si-Si distance in organodisilanes (2.35 A) and the Si-B distances [2.017(3) to 2.116(3) A] are very close to the sum of the covalent radii of the two atoms (2.07 A). Further derivatives with disilaborane cluster geometry are known for the phenyl substituted compounds l,2-Ph2-doso-l,2-Si2B1oH1o and l-Me-2-Ph-doso-l,2-Si2BioHi0 [6, 7]. In addition to these disila-doso-dodecaborane clusters one example with two different group 14 elements as a part of the cluster core is known. In Scheme 3.3-2 the synthesis of this sila-stanna-doso-dodecaborate is shown. The structure of this heteroborate was determined in the solid state and the Si-Sn distance is 2.608(4) A (Scheme 3.3-2) [8]. 

In essence, then, the electronic environment of the silicon can be described by a substituent value, o-Si, which is (a) equal to the Taft a if the substituent is an alkyl group, (b) equal to the Hammett a if the substituent is phenyl or substituted phenyl, and (c) for substituents bearing unshared electron pairs close to the silicon, each values computed in this study appear in Table II. 

For the first time the proposed cationic pentacoordinated structure in solution could be confirmed for the solid state by a X-ray structure determination (Fig. 3), which shows clearly the ionic structure of bis[2-(dimethylaminomethyl)phenyl]silyl triflate 12. The coordination geometry around silicon is that of a nearly ideal trigonal bipyramidal structure with both dimethylamino groups occupying the axial positions (Si-N 205.2 and 207.2 pm). 

The type of analysis utilized to determine the composition of a pyrolysate is important because only a certain group of compounds can be seen in one type of analysis. The identification of more volatile compounds found in cellulose pyrolysate can be done very conveniently by on-line Py-GC/MS analysis. The TIC traces of cellulose pyrolysate obtained at 590° C and separated on a Carbowax or on a methyl-phenyl silicone type column were already given in Section 5.2 (Figures 5.2,10, 5.2.11 and 5.2.13). As indicated in Section 5.2, in these chromatograms compounds such as formaldehyde, methanol, or CO were not seen because the mass spectrometer used for the analysis had the mass range detection with a low cut-off at m/z = 32. 

Lithium aluminium dibutylamide has been used165 as a titrant for the determination of silanols. Silanol hydroxy groups were titrated in monomeric and polymeric silanols, and in silicone resins, using Af-phenyl-4-phenylazoaniline as indicator. 

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