Sigma compounds

Figure C3.2.7. A series of electron transfer model compounds with the donor and acceptor moieties linked by (from top to bottom) (a) a hydrogen bond bridge (b) all sigma-bond bridge (c) partially unsaturated bridge. Studies with these compounds showed that hydrogen bonds can provide efficient donor-acceptor interactions. From Piotrowiak P 1999 Photoinduced electron transfer in molecular systems recent developments Chem. Soc. Rev. 28 143-50.

Sigma-Nicolet ftk 10,400 PC-based compounds found in Sigma catalog... 

Rhodacarborane catalysts have been immobilized by attachment to polystyrene beads with appreciable retention of catalytic activity (227). A 13-vertex /oj iJ-hydridorhodacarborane has also been synthesized and demonstrated to possess catalytic activity similar to that of the icosahedral species (228). Ak-oxidation of closo- >(2- P((Z [) 2 - i- > l[l-Bih(Z, results in a brilliant purple dimer. This compound contains two formal Rh " centers linked by a sigma bond and a pak of Rh—H—B bridge bonds. A number of similar dimer complexes have been characterized and the mechanism of dimer formation in these rhodacarborane clusters have been studied in detail (229). 

Type 315-This has a composition that provides a similar oxidation resistance to type 309 but has less liability to embrittlement due to sigma formation if used for long periods in the range of 425 to 815°C. (Sigma phase is the hard and brittle intermetallic compound FeCr formed in chromium rich alloys when used for long periods in the temperature range of 650 to 850°.)... 

Figure 10 Comparison of hardness 3 sigma variability ratings fluoroelastomer compound.

A compound of chlorine and fluorine, CIF, reacts at about 75°C with uranium to produce uranium hexafluoride and chlorine fluoride, C1F. A certain amount of uranium produced 5.63 g of uranium hexafluoride and 457 mL of chlorine fluoride at 75°C and 3.00 atm. What is x Describe foe geometry, polarity, and bond angles of foe compound and foe hybridization of chlorine. How many sigma and pi bonds are there ... 

In addition to the reactions of luciferin shown in Fig. 7.2.3, Trainor (1979) made an interesting discovery that arylsulfatase from Pattela vulgata (Sigma) converts luciferin into a violet compound (treatment conditions pH 5.05, 37°C, 4 hr). The compound showed absorption peaks at 344 nm and 560 nm (Fig. 7.2.7), and the peaks shifted reversibly to 347 nm and 547 nm in acid, and to 364 nm and 720 nm in an alkaline solution. The violet compound was also obtained from the pink compound by treatment with arylsulfatase, or from luciferin by heating in 50% trifluoroacetic acid at 100°C for 1 hr, followed by an addition of oxygenated water. These results, together with the... 

Pi and Sigma Transition Metal Carbon Compounds as Catalysts for the Polymerization of Vinyl Monomers and Olefins... 

Compounds and Other Sigma-Bonded Metal Compounds Based on Metal Vapor as a Reagent. 203... 

A new synthesis for sigma-bonded, metal alkyls and similar compounds, involving a reaction between metal vapor and free radicals generated in a radio-frequency glow-discharge, has been reported (35). 

Purity levels of commercial preparations have also been estimated based on their Cu contents and compared with the theoretical values expected for fuUy coppered chlorophyllin based on the two major compounds Cu(ll) chlorin e4 (disodium salt) and Cu(ll) chlorin e6 (trisodium salt). The expected theoretical content of copper in a pure Cu chlorophyllin complex is 9.2%, which has never been found in commercial preparations. The sodium copper chlorophyllin from Sigma-Aldrich (St. Louis, MO) has a 4.5% copper content, specified by the manufacturer with respect... 

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