The influence of chelation

The influence of chelation. Some acids are capable of forming internal hydrogen bonds, and the carbonyl frequency is reduced accordingly. Of nine acids recorded by Flett [9] as having carbonyl frequencies below 1680 cm , seven are of this type. The simplest case is that of fumaric acid, which absorbs at 1680 cm , in contrast to the normal value of 1705 cm of maleic acid [9]. orZ/zo-Hydroxybenzoic acids [8] can chelate in a similar way to the ort/zo-hydroxyacetophenones and ort/io-hydroxybenzaldehydes, with a correspondingly large shift of the carbonyl frequency. 

Salicylic acid absorbs at 1655 cm , and this is comparable with the shifts experienced with the 0-hydroxy-aj3-unsaturated ketones. 3-Amino-aj3-unsaturated acids also show this effect, as is to be expected. 3-Amino-2-naphthoic acid absorbs at 1665 cm Flett [9], and Musso [75] quote a number of other similar cases. We have also observed a case of this type with N-phenylanthranilic acid, in which the carbonyl absorption occurs at 1660 cm .  

In the consideration of carbonyl frequencies of hydroxy-, amino-or ketonic acids, allowances must also be made for the possibility that ring closure has occurred with the formation of a lactone, lactam or lactol. The characteristic carbonyl frequency of the carboxyUc acid then disappears. Penicillic acid [28] has been shown to be such a case, and it exists as a free acid only under certain limited physical conditions. Similarly, acetophenone ort/zo-carboxylic acid absorbs at 1732 cm . This corresponds to a five-membered ring lactol frequency rather than that of an aryl acid. ort/zo-Formylbenzoic acid (1738 cm also exists as the lactol rather than as the free acid [17], and numerous other cases are known. In some cases, such as benzil-ort/io-carboxylic acid, both forms are known. The keto-form has absorptions at 1698 cm and 1683 cm , corresponding to the aryl ketone and to the acid, whilst the lactol form absorbs at 1692 cm and 1745 cm , corresponding to the aryl ketone and the five-membered ring lactol carbonyl absorption. 

Schotte and Rosenberg [76, 77] have also studied dicarboxylic acids, particularly in relation to the stereoisomerism of aa -di-substituted compounds. Minor differences occur between the 

The intensity. Carbonyl absorptions from carboxylic acids are generally more intense than those of ketones. Cross and Rolfe [29] quote values for the molecular extinction coefficients of a number of acids, and show that they are about twice the values for the corresponding ketones. Flett [9,99] has also given a good deal of data on intensities of the dimer bands. It is clear that there are distinct differences between various classes, but the assessment of absolute intensities is especially difficult in view of the problems of monomer/dimer equilibrium and of the effects of changes of phase or of solvent. It is therefore very doubtful whether intensity measurements have much to offer for diagnostic purposes. 

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Several studies have been undertaken in an attempt to understand factors that affect the susceptibility of a complex to reductive elimination. These include investigations on Me-Pd-CNC pincer complexes [39] studies on the influence of the geometry of the complexes [40] the impact of A-substituents [41] and a study on the influence of chelating spectator ligands in complexes of the type [PdMe(NHC) (P-P)]BF [42]. 

Diimide reduction of TPP (33) led to TPC (42) and TPBC (34), contaminated by no more than 2-4% of TPiBC (35). A remarkable feature is the influence of chelated zinc on the regioselectivity of this reaction. Zn-TPC (25)... 

Coulier, L., V. H. J. de Beer, J. A. R. van Veen, and J W. Niemantsverdriet, Correlation between Hydrodesulfurization Activity and Order of Ni and Mo Sulfidation in Planar Silica-Supported NiMo Catalysts the Influence of Chelating Agents , J. Catal 197, Issue 1,1 January 2001, pp 26-33. 

Additions of enol silanes to p-alkoxy aldehyde (85 equation 25) are reported in Table 17. High selectivity (chelation control) was obtained with TiCU via complex (78 entries 1, 2). The same preference for isomers (86) and (87) was obtained with BF3 via complex (80), which simulates chelation. The influence of chelation on simple stereoselection is also evident in the reactions of achiral aldehydes (90) and (92) with silyl enol ethers (Z)-(91) and ( )-(93), which are usually moderately anti selective in their reactions with aldehydes incapable of chelation high syn selectivity was obtained irrespective of the enol ether geometry (equations 26 and 27). - ... 

Bhattacharya and coworkers, Reed and Nonavinakere, and Rubin and Mercer smdied the influence of chelating agent EDTA on the adsorptive removal of Cd(n) from aqueous solutions by activated carbons. Although Rubin and Mercer found little effect of the chelating agent on the adsorption, Bhattacharya and coworkers did find an inaease in adsorption in the presence of EDTA, at least in the case of basic carbons. These coworkers even proposed the formation of an electron donor-acceptor... 

Hultin, T., Ostner, U. Specific unmasking of ribosomal proteins under the influence of chelating agents and increased ionic strength. Biochim. biophys. Acta (Amst.) 160, 229-238 (1968)... 

Zilberberg et al. reported the influence of chelated cisplatin complex with guanine(06d 7) on Watson-Crick base pairing (Zilberberg et al. 1997). In such chelate structures, more distinct perturbation of base pairing was revealed. However, such chelate binding pattern is imUkely to be relevant to real ds-DNA conditions. 

Influence of transport and reaction on wormhole formation in porous media. AICHE Journal. September 1933-1949. C. N. Fredd and H. S. Fogler. 1998. The influence of chelating agents on the kinetics of calcite dissolution. JWrwi / (f Colloid and Interface Science. 204 187-197. Fredd,... 

The chelated calcium cementing materials are suppHed as two-part paste products. In use, equal parts of the two pastes are thoroughly mixed together to give a fluid mass that can be appHed without pressure over an exposed tooth pulp or in a deep-seated cavity. Under the influence of the oral temperature and humidity, the fluid mass sets to a hard, strong, therapeutic protective seal. 

The lower diastereoselectivity found with aldehyde 15 (R = CH3) can be explained by the steric influence of the two methyl substituents in close vicinity to the stereogenic center, which probably diminishes the ability of the ether oxygen to coordinate. In contrast, a significant difference in the diastereoselectivity was found in the additions of phenyllithium and phenylmagnesium bromide to isopropylidene glyceraldehyde (17)58 (see also Section 1.3.1.3.6.). Presumably the diastereo-sclcctivity of the phenyllithium addition is determined by the ratio of chelation-controlled to nonchelation-controlled attack of the nucleophile, whereas in the case of phenylmagnesium bromide additional chelation with the / -ether oxygen may occur. Formation of the -chelate 19 stabilizes the Felkin-Anh transition state and therefore increases the proportion of the anZz -diastereomeric addition product. 

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

In order to improve the selectivity toward the formation of 1,3-PDO, we studied the influence of metal salt additives. While the addition of calcium or copper salts exhibited a moderate influence, the presence of iron salts played a significant role on the rate and selectivity of the reaction (Figure 35.1). The metal additives reduced noticeably the activity of the rhodium catalysts suggesting that they acted as a surface poison, but they modified the selectivity of the glycerol hydrogenolysis, probably through selective diol chelation. 

For enolates with additional functional groups, chelation may influence stereoselectivity. Chelation-controlled alkylation has been examined in the context of the synthesis of a polyol lactone (-)-discodermolide. The lithium enolate 4 reacts with the allylic iodide 5 in a hexane THF solvent mixture to give a 6 1 ratio favoring the desired stereoisomer. Use of the sodium enolate gives the opposite stereoselectivity, presumably because of the loss of chelation.61 The solvent seems to be quite important in promoting chelation control. 

Roels HA, Balis-Jacques MN, Buchet J-P, et al. 1979. The influence of sex and of chelation therapy on erythrocyte protoporphyrin and urinary delta-aminolevulinic acid in lead-exposed workers. J Occup Med 21 527-539. 

The book focuses on three main themes catalyst preparation and activation, reaction mechanism, and process-related topics. A panel of expert contributors discusses synthesis of catalysts, carbon nanomaterials, nitric oxide calcinations, the influence of carbon, catalytic performance issues, chelating agents, and Cu and alkali promoters. They also explore Co/silica catalysts, thermodynamic control, the Two Alpha model, co-feeding experiments, internal diffusion limitations. Fe-LTFT selectivity, and the effect of co-fed water. Lastly, the book examines cross-flow filtration, kinetic studies, reduction of CO emissions, syncrude, and low-temperature water-gas shift. 

Fig. 15. Trends illustrating the influence of the arene, the chelate, and the leaving group on the cytotoxicity and cross-resistance of ruthenium-arene complexes developed in the Sadler lab. The complexes are not cross-resistant with cisplatin.

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