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Silicon Compounds (silicon + compound)

Distribution by Scientific Domains

Chemistry	83%

Selected Abstracts

TEOS,colloidal silica,PDMS-OH hybrid formulation used for stone consolidation

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2010
Carmen Salazar-Hernández
Abstract The consolidation of materials concept, which consists of introducing a chemical substance (consolidant) into degraded stone, has been applied to architectural conservation. Silicon compounds such as tetraethoxysilane (TEOS) are frequently used as a base for commercial consolidant formulations due to their ability to form a siloxane polymer such as SiO2. However, the silica xerogels deposited into the stone show poor performance and the gels obtained are non-porous and tend to crack during the drying stage. In order to avoid the fractures and to improve gel properties, we propose the synthesis of a hybrid consolidant based on TEOS and fillers such as colloidal silica (200 nm in diameter) and hydroxy-terminated polydimethylsiloxane (PDMS-OH). Both additives enhance gel properties such as porosity and elasticity, leading to the formation of non-fractured and permeable gels. Characterization of the hybrid xerogel was carried out by nitrogen adsorption and 29Si MAS-NMR. The properties of the hybrid xerogels were compared with those prepared from a formulation based on TEOS (T-ME) with a composition similar to a commercial product. In order to evaluate the effectiveness of the hybrid consolidant, it was applied to tuff-stone of historical monuments in the city of Guanajuato, Mexico. The tuff-stone was also treated with the formulation T-ME. Both treatments were studied by determining the percentage of consolidant deposited, evaluating changes in porosity and hardness of the treated stone. The applicability of the hybrid consolidant for the decayed tuff-stone is under study. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Connectivities in molecules by INADEQUATE: recent developments,

MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2002
J. Buddrus
Abstract The INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment) consists of a pulse sequence which eliminates the NMR signals from isolated spins (spin system A) displaying signals from coupled spins (spin system AX or higher spin systems). It is of great importance when applied to molecules with skeleton elements such as carbon, silicon or tungsten, all of which contain a small percentage of spin-½ isotopes embedded in magnetically inactive isotopes. Analysis of the AX type spectra gives one-bond and long-range coupling constants (see compound 6) and, most important, the connectivity pattern of the skeleton atoms in molecules of unknown structure such as the carbon compounds 1 or 2, the silicon compound 3 or the lithium compound 4b. Unfortunately, INADEQUATE is rather insensitive, in the case of carbon only one out of 104 molecules gives the desired response. Efforts to reduce this drawback are described; recently, a remarkable step forward has been made by concentrating the four lines of an AX spin system to just two signals (see Fig. 2). Copyright © 2001 John Wiley & Sons, Ltd. [source]

Disproving a Silicon Analog of an Alkyne with the Aid of Topological Analyses of the Electronic Structure and Ab Initio Molecular Dynamics Calculations

CHEMPHYSCHEM, Issue 9 2005
Carlo A. Pignedoli Dr.
Abstract A silicon compound has recently been synthesized that was claimed to exhibit the first realization of a silicon,silicon triple bond. We debate this classification on the basis of a thorough investigation of the nature of the chemical bond, using the rigorous topological analysis of the electron density as developed in Bader's atoms-in-molecules theory, that of the electron localization function and the related orbital-independent definitions of the bond order. Our results refer both to the ground-state geometry and to nonequilibrium configurations, which are accessed by the system in a room-temperature ab initio molecular dynamics simulation. We also use the reciprocal compliance force constant as an independent chemical descriptor. All the above procedures are in agreement and do not support the classification of the silicon,silicon central bond as triple. The characterization which consistently emerges from the present study is one in which two electron pairs participate in the bonding and the other pair belongs mainly to nonbonding regions. [source]

Control of stereochemical structures of silicon-containing polymeric systems,

POLYMER INTERNATIONAL, Issue 3 2009
Yusuke Kawakami
Abstract Various optically active silicon compounds have been synthesized or separated, and used to synthesize silicon-containing polymers with well-controlled stereochemical structures. Hydrosilylation, anionic ring-opening polymerization and cross-coupling reactions have been used to synthesize optically active and/or stereoregular silicon-containing polymers. Copyright © 2009 Society of Chemical Industry [source]

Disila-Okoumal: A Silicon Analogue of the Ambergris Odorant Okoumal

CHEMBIOCHEM, Issue 12 2007
Matthias W. Büttner
Abstract Two-fold sila-substitution (C/Si exchange) in the saturated ring of the tetrahydronaphthalene skeleton of the ambery odorant okoumal (5) provides disila-okoumal (6). The okoumal isomers 5,a,d were synthesized from 1-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthyl)ethanone (7), and the silicon analogues 6,a,d were synthesized from 1-(5,5,8,8-tetramethyl-5,8-disila-5,6,7,8-tetrahydro-2-naphthyl)ethanone (8). Detailed olfactory properties of 5,a,d and 6,a,d are reported, together with the respective threshold values. All enantiomers of okoumal and disila-okoumal exhibit typical ambery odor notes with woody facets, as is characteristic of okoumal and karanal, but a stereocenter at the 2-position was found to be of utmost importance for the odor thresholds; the lowest value of 0.31 ng per L air was measured for the 2R -configured silicon compounds 6,a and 6,c. [source]

Neutral Pentacoordinate Silicon(IV) Complexes with Silicon,Chalcogen (S, Se, Te) Bonds

CHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2009
Bastian Theis Dipl.-Chem.
Abstract The neutral pentacoordinate silicon(IV) complexes 1 (SiS2ONC skeleton), 2 (SiSeSONC), 3 (SiTeSONC), 6/9 (SiSe2O2C), 7 (SiSe2S2C), and 8/10 (SiSe4C) were synthesized and structurally characterized by using single-crystal X-ray diffraction and multinuclear solid-state and solution-state (except for 6,9) NMR spectroscopy. With the synthesis of compounds 1,3 and 6,10, it has been demonstrated that pentacoordinate silicon compounds with soft chalcogen ligand atoms (S, Se, Te) can be stable in the solid state and in solution. [source]