Carbonate group

Polyesters. Polyesters containing carbonate groups have been prepared from this diol (see Polycarbonates) (99). Films of this polymer, formed from an acetone or ethyl acetate solution, exhibit exceUent adhesive properties. 

The----CH2----group is twice joined hy a single bond to a carbon group,... 

Diphenyl carbonate, an alternative source of the carbonate group to phosgene, may be obtained by reacting phenol with phosgene in acqueous caustic soda solution, the reaction being accelerated by tertiary amines. The diphenyl carbonate can be purified by redistillation. 

The carbonate groups are polar but separated by aromatic hydrocarbon groups. 

Figure 20.6 shows the disposition of the molecules in the elementary cell as detennined by Prietschk. It will be seen that in the crystalline zone the molecules pack in such a way that the methyl groups attached to the pivotal carbon atom extend toward the back of the carbonate group of the neighbouring chain. 

These materials have the general structure shown in Figure 20.11 and are prepared by reaction of bisphenol A with iso- and/or terephthalic acid and a carbonate group donor (e.g. phosgene or diphenyl carbonate). 

Finally mention may be made of the phenoxy resins. These do not contain the carbonate group but are otherwise similar in structure, and to some extent in properties, to the bis-phenol A polycarbonate. They are dealt with in detail in Chapter 21. 

Burchell, T.D., Weaver, C E., Derbyshire, F., Fei, Y.Q. and Jagtoyen M., Carbon fiber composite molecular sievesisynthesis and characterization. In Proc. Carbon 94, Granada, Spain, Spanish Carbon Group, 1994, pp. 650 651. 

Fig. 2. Fully hydrated calcile lOT 1 surface showing rotation of surface carbonate groups with bulk ordering below (after [6]).

The reactivity of various steroid alcohols decreases in the order primary > secondary (equatorial) > secondary (axial) > tertiary. The only systematic investigation relating to the selective protection of steroidal hydroxyl functions has been carried out with the cathylate (ethyl carbonate) group. Since only equatorial hydroxyl groups form cathylates this ester has been used as a diagnostic tool to elucidate the configuration of secondary alcohols. 

Mn-+ K+ Ni " Arginase Pyruvate kinase (also requires Mg ) U rease Tetrahydrofolate (THF) Other one-carbon groups Thymidylate synthase... 

We are familiar with several examples of chemical activation as a strategy for group transfer reactions. Acetyl-CoA is an activated form of acetate, biotin and tetrahydrofolate activate one-carbon groups for transfer, and ATP is an activated form of phosphate. Luis Leloir, a biochemist in Argentina, showed in the 1950s that glycogen synthesis depended upon sugar nucleotides, which may be... 

MC has a much stronger influence on ion-pair dissociation than PC. The EO units on MC coordinate cations which have been dissociated by the carbonate group, and prevent cation association with the anion. It is thought that, whereas conventional plasticizers like PC create fast ion-... 

Dihydrofolate reductase is required for the sythesis of tetrahydrofolate, a co-factor required for the transfer of single carbon groups. Inhibition of dihydrofolate... 

Effect on Reactivity. We refer to the carbon containing the nucleofuge (X) as the a carbon and to the carbon that loses the positive species as the p carbon. Groups attached to the a or P carbons can exert at least four kinds of influence ... 

Decane and other hydrocarbons consist of chains of tetrahedral carbon groups, emphasized here by highlighting one of the groups. 

Figure 5.10. Defects consisting of oxygen vacancies constitute adsorption sites on a Ti02 (110) surface. Note how CO binds with its lone-pair electrons on a Ti ion (a Lewis acid site). O2 dissociating on a defect furnishes an O atom that locally repairs the defect. CO2 may adsorb by coordinating to an O atom, thus forming a carbonate group. [Figure adapted from W. Gopel, C. Rocher and R. Feierabend, Phys. Rev. B 28 (1983) 3427.]...

The role of the ligands is both to stabilize the Pd(0) state and to tune the reactivity of the palladium. The outline mechanism above does not specify many detailed aspects of the reaction that are important to understanding the effect of ligands, added salts, and solvents. Moreover, it does not address the stereochemistry, either in terms of the Pd center (tetracoordinate pentacoordinate , cisl, transl) or of the reacting carbon groups (inversion , retention ). Some of these issues are addressed by a more detailed mechanism.190... 

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