Carbonate-bound

Quantitative Analysis of All llithium Initiator Solutions. Solutions of alkyUithium compounds frequentiy show turbidity associated with the formation of lithium alkoxides by oxidation reactions or lithium hydroxide by reaction with moisture. Although these species contribute to the total basicity of the solution as determined by simple acid titration, they do not react with allyhc and henzylic chlorides or ethylene dibromide rapidly in ether solvents. This difference is the basis for the double titration method of determining the amount of active carbon-bound lithium reagent in a given sample (55,56). Thus the amount of carbon-bound lithium is calculated from the difference between the total amount of base determined by acid titration and the amount of base remaining after the solution reacts with either benzyl chloride, allyl chloride, or ethylene dibromide. 

The double titration method, which involves the use of ben2ylchloride, 1,2-dibromoethane, or aUyl bromide, determines carbon-bound lithium indirectly (101,102). One sample of the //-butyUithium is hydroly2ed directly, and the resulting alkalinity is determined. A second sample is treated with ben2ylchloride and is then hydroly2ed and titrated with acid. The second value (free base) is subtracted from the first (total base) to give a measure of the actual carbon-bound lithium present (active base). 

The oxidimetric method, which involves the use of soUd vanadium pentoxide as oxidant (103). The vanadium is reduced quantitatively by butyUithium and is determined potentiometricaUy by titration with standard sulfatoceric acid [17106-39-7]. This method gives a direct measure of the actual carbon-bound lithium present when compared to the total titrated alkalinity. 

Tiichloiomethanesulfenyl chloiide can be reduced to thiophosgene by metals in the presence of acid and by various other reducing agents. The sulfur-bonded chlorine of trichloromethanesulfenyl chloride is most easily displaced by nucleophilic reagents, but under some conditions, the carbon-bound chlorines are also reactive (54). 

The symbols f and f correspond to total fraction of and hybridi2ed carbon, respectively, f represents the fraction of carbon in aromatic rings f , the fraction in carbonyls, b > 165 ppm the aromatic fraction that is protonated the aromatic fraction that is nonprotonated f, the phenoHc or phenohc ether carbon, 6 = 150-165 ppm f, the alkylated aromatic carbon, 6 = 135-150 ppm , the aromatic bridgehead carbon f represents the fraction of CH or CH2 aUphatic carbon f, the CH or nonprotonated aUphatic carbon and f, the aUphatic carbon bound to oxygen, b — 50-90 ppm. 

Cadmium-magnesium alloy (Cd5Mg5), calculation of thermodynamic quantities, 136, 142 Cadmium-tin alloy (Cd5Sn5), calculation of thermodynamic quantities, 136 Carbanion, 180 Carbon bound, 367... 

Recognition of the fact that tin(IV) enolates exist predominantly as the carbon-bound enolate has led to the alternative suggestion that a four-center transition state, such as L could also rationalize the reversal of diastereoselectivity upon changing the enolate counterion from aluminum to tin26-44. 

Reaction of [Ir(cod)Cl]2 with (6-methyl-2-pyridyl)methyl lithium yields the binuclear species [(cod)Ir(/i-CH2-py-6-Me-C, /V)]2, (401). The Ir centers in (401) are 3.5889(3) A apart, indicating little metal-metal interaction. Treatment of (401) with PPh2Et yields [(cod)Ir(PPh2Et)2(CH2-py-6Me)], which contains the monodentate, carbon-bound pyridylmethyl ligand. 

There is also evidence that single, carbon-bound fluorine substituents, particularly when on an aromatic ring, can exhibit specific polarity influences, including H-bonding, that can strongly influence binding to... 

However, CFC13 has the advantage that its presence will not have any influence upon a compound s chemical shifts, plus its observed signal lies substantially downfield of most signals deriving from carbon-bound fluorine. Therefore, most fluorine chemical shifts (5) are negative in value. 

Figure 2.1 provides a quick overview of the basic chemical shift ranges for carbon-bound F, CF2, and CF3 substituents. Specific details... 

Whether bound directly to the silicon or on a carbon bound to the silicon, a fluorine substituent within a silane is highly shielded compared to that in a hydrocarbon. For example, the fluorine of TMS fluoride absorbs more than 25-ppm upfield from that in t-butyl fluoride (Scheme 3.28). (For additional data on Si—F compounds, see Chapter 7, which deals with compounds that have heteroatom-fluorine bonds.)... 

Likewise, a primary —CH2F fluorine adjacent to silicon is shielded by more than 50 ppm compared to the respective hydrocarbon (Scheme 3.29), with the value of -277ppm observed for fluoromethyltrimethyl-silane being the largest chemical shift known for a single carbon-bound fluorine. 

Trifluoromethyl groups bound to a carbon-carbon triple bond absorb at the lowest field of any carbon-bound CF3 group, with 3,3,3-trifluoropro-pyne having a 5h of-52 (Scheme 5.40). When the CF3 group is one carbon farther from the triple bond, it is almost unaffected by its presence. 

The equatorial fluorines of these nitrogen-bound SF3 groups are greatly deshielded as compared to those in their carbon-bound counterparts in Scheme 7.13. 

Other even more cunning methods have been devised to suppress the water signal in samples that have a large water content (e.g., bio-fluid samples) such as the WET and the WATERGATE pulse sequences. Other sequences have been devised to cope with signals from carbon-bound hydrogens. Some of these actually collapse the 13C satellites into the main 12C peak prior to suppression. Such a sequence would be useful if you were forced to acquire a spectrum in a nondeuterated solvent. 

The carbonate-bound trace elements are usually extracted by NaOAc-HOAc (Tessier et al., 1979 Hickey and Kittrick, 1984 Banin et. al., 1990 and Han et al., 1992) or by using chelating agents, such as EDTA (Sposito et al., 1982 Emmerich et al., 1982 Miller and Mcfee, 1983 Chang et al., 1984 Knudtsen and O Connor, 1987 McGrath and Cegarra, 1992). Generally, EDTA lacks the required specificity and selectivity for carbonate phase extractions and tends to extract metals from a number of soil components. 

The cumulative sums of selected major and trace metals extracted by the two SSD procedures from representative arid-zone soils are shown in Fig. 4.6. As can be seen from the figure, the Rehovot procedure is stronger in attacking desired fractions, such as the carbonate bound, Mn oxide bound and organically bound fractions. Extraction of certain major elements, indicating selectivity, specificity and completeness of extraction of given soil components, was found to differ between the two procedures. Calcium and Mg were more completely extracted from the carbonate fraction in arid zone soils by the Rehovot procedure. Calcium and relevant trace elements bound in the carbonate fraction, which were not completely dissolved by the Bonn procedure at this step, were released at the following steps, such as the ERO, OM or RO fractions. 

Trace elements can be adsorbed on the surface of calcite, influencing their solubility in calcareous soils of arid and semi-arid zones. The carbonate bound fraction is the major solid-phase component for many trace elements (Cd, Pb, Zn, Ni and Cu) in arid and semi-arid soils, especially in newly contaminated soils (Table 5.3). In Israeli arid soils treated with metal nitrates, the carbonate bound fraction is the largest solid-phase component (60-80%, 50-60%, 40-60%, 30-40%, and 25-36% for Cd, Pb, Zn, Ni, and Cu respectively). Divalent metallic cations at low aqueous concentrations first associate with calcite via adsorption reactions. Then they may be incorporated into the calcite lattice as a co-precipitate by recrystallization (Franklin and Morse, 1983 Komicker et al., 1985 Davis et al., 1987 Zachara et al., 1988 Reeder and Prosky, 1986 Pingitore and... 

Cadmium in native arid soils predominates in the carbonate fraction. In 45 uncontaminated Israeli soils, Cd is mainly present in the carbonate bound fraction (43.5% 22.3%), followed by the easily reducible oxide bound fraction (22% 19.5%) (Table 5.4) (Banin et al., 1997a). The... 

In Californian soils amended with sewage sludge for seven years, Ni is mostly present in the residual (64%), the organically bound (12%) and the carbonate fractions (18%) (Chang et al., 1984). Nickel in the carbonate fraction is found to increase with time in arid zone soils amended with sludge (Knudtsen and O Connor, 1987). In the sludge-amended calcareous soils of Southeast Spain, the residual and the carbonate bound Ni fractions are the major solid-phase (Moral et al., 2005). 

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