Structure carboxylates

Common Name 2-piperidinoethyl 3-methylflavone-8-carboxylate Structural Formula ... 

Acylamino)-substituted carboxylate esters and amides can be alkylated with good anti-2,4 stereoselectivity using two equivalents of a strong base. The stereoselectivity is independent of the steric bulk of the remainder of the carboxylate structure. Propose a TS that is consistent with these observations. 

The basic zinc carboxylate structure with a Zn40 core is now well characterized structurally with a number of examples.371 It can also form part of higher nuclearity structures and coordination networks.372,373... 

Trinuclear zinc carboxylate structures of the form MZn2(MeCH=CHC02)6(quinoline)2 have been structurally characterized with M = Mn, Co, Ni, Zn, Cd, Mg, Ca, Sr. Structural variation is observed for the group 2 metals. The remaining complexes all show linear trimers with the central metal atom octahedrally coordinated and linked to each zinc by two bidentate and one mono-dentate carboxylate.377 A basic benzoate octanuclear structure with four vanadium(III) and four zinc atoms has been characterized, [VZnO(benzoate)3(TF[F)]4-2TnF.378... 

EtO)2P(S)] with short oxide bonds and phosphate oxygen weakly bridging to the second tin. This relates to the carboxylate structure of (26b) where the additional bridges are weaker. 

Calcium, Ca 6-8, flexible O-Carboxylate, Structure, charge carrier. 

Zinc, Zn + (d °) 4, tetrahedral O-Carboxylate, Structure in zinc fingers. 

Zinc, Zn"" ( / ) 5, square pyramid O-Carboxylate, Structure in hydrolases. 

All reported trinuclear complexes possessing oxide bridges which have been characterized to date have been prepared from Mn04 in either aqueous or non-aqueous media, and possess the "basic carboxylate" structure viz. a / 3-oxide-centered Mna triangle. Both Mn Mn2 and Mns species are currently known, and their pertinent structural parameters are listed in Table II. 

A large number of carboxylate structures have been unambiguously determined by diffraction methods. This must be the preferred physical technique for all carboxylates and is essential for those complexes which do not fall clearly within one of these seven modes of bonding. In addition to... 

Scheme 7 Examples of different carboxyl structures in cellulose...

Ketones and nitriles are rather soft bases their coordination onto electron-deficient sites on oxides is, therefore, relatively weak. One may, however, expect an improved specificity of chemisorption due to their softness. Unfortunately, however, these substances very easily undergo chemical transformations at oxide surfaces. Thus, carboxylate structures are formed on adsorption of acetone on alumina (194, 245-247), titanium dioxide (194), and magnesium oxide (219, 248, 249). Besides, acetone is also coordinated onto Lewis acid sites. A surface enolate species has been suggested as an intermediate of the carboxylate formation (248, 249). However, hexafluoroacetone also leads to the formation of trifluoroacetate ions (219). The attack of a basic surface OH ion may, therefore, be envisaged as an alternative or competing reaction path ... 

One important chemical result from the ESCA studies involves the formation of surface carboxylates. Upon transfer of the monolayer to silver, the formation of a carboxylate could be detected by the production of a single peak in the oxygen Is line due to equivalent oxygens in the carboxylate structure. Since the oxygen spectrum of the monolayer yields near stoichiometric C-0/C==0 ratio of 1, the carboxylate is not detectable. Studies with monolayer films of cadmium arachidate indicated detectability of the carboxylate as a single carbon Is peak. The lack of the formation of this interfacial carboxylate indicates the strength (or weakness) of surface chemistry which occurs on this silver surface as prepared. 

All reported trinuclear manganese-oxide complexes possess the so-called basic carboxylate structure (Fig. 17) (62, 301-303). The three metals are disposed in a triangle with a central /z3-oxide in (or approximately in) the Mn3 plane two carboxylates bridge each pair of Mn, while the last coordination site on each metal is filled by a terminal donor ligand such as pyridine, imidazole, or water. This arrangement... 

Mahieu et al. (1999) conducted a similar statistical survey of the NMR spectra of several hundred whole soils and soil size fractions, soil-derived HAs and FAs, and aquatic FAs. They used four structural subunits carbonyl— 160-220 ppm aromatic—110-160 ppm O-alkyl—50-110 ppm and alkyl—0-50 ppm. Their carbonyl subunit includes the carbonyl and carboxyl structural subunits used in this review, and their boundary between alkyl and 0-alkyl subunits is 50 ppm, rather than 60 ppm. For the 31 aquatic FAs in that study, the mean percentages of carbonyl, aromatic, O-alkyl, and alkyl carbon were 24%, 21%, 20%, and 35%, respectively. These percentages are very close to the mean values in Figure 7 for FAs in freshwaters (21%, 25%, 23%, and 32%, respectively). The degree to... 

The spectra of the annealed carbons (D—H, D—N) (Fig. 4) confirm the observation that heat treatment under vacuum or in ammonia diminishes the content of oxygen surface complexes, especially that of strongly acidic surface groups. There the band typical of carboxylic structures disappears and the bands of the remaining surface oxygen complexes are much reduced. 

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