Bridge groups

A bridging group should be indicated by adding the Greek letter p immediately before its names and separating this from the rest of the complex by a hyphen. The atom or atoms of the characteristic element to which the bridging atom is bonded, is indicated by numbers. 

Substantial decomposition of phenoHc resins begins above 300°C. In the presence of oxygen, the methylene bridging group is converted to a hydroperoxide which in turn yields alcohols and ketones on decomposition. 

Dihydroxyethyleneurea (DHEU) (6) is also a cross-linker, but is extremely vulnerable to hydrolysis in an alkaline home laundering. Another approach toward formaldehyde-free agents has been the use of glyoxal in the bridging group between cycHc DHEU and related ring systems (108). 

The stmcture of activated carbon is best described as a twisted network of defective carbon layer planes, cross-linked by aHphatic bridging groups (6). X-ray diffraction patterns of activated carbon reveal that it is nongraphitic, remaining amorphous because the randomly cross-linked network inhibits reordering of the stmcture even when heated to 3000°C (7). This property of activated carbon contributes to its most unique feature, namely, the highly developed and accessible internal pore stmcture. The surface area, dimensions, and distribution of the pores depend on the precursor and on the conditions of carbonization and activation. Pore sizes are classified (8) by the International Union of Pure and AppHed Chemistry (lUPAC) as micropores (pore width <2 nm), mesopores (pore width 2—50 nm), and macropores (pore width >50 nm) (see Adsorption). 

Reactive dyes coasist basically of three compoaeats a dye, a bridging group (B), and the reactive group (R), dye—B—R. The reactive group may be considered ia two parts as a carrying group and the reactive component. 

The stereochemistry of chlorination can be explained in similar terms. Chlorine would be expected to be a somewhat poorer bridging group than bromine because it is less polarizable and more resistant to becoming positively charged. Comparison of the data for bromination and chlorination of E- and Z-l-phenylpropene confirms this trend (see Table 6.2). Although anti addition is dominant in bromination, syn addition is slightly preferred... 

Polymers containing long alkyl side chains, typically between 16 and 22 carbon atoms in length, have been used extensively as low adhesion backsizes for PSA tape products for many years. The general structure of such polymers is shown schematically in Fig. 8. The alkyl side chains are attached through a bridging group, R, to the polymer backbone, and the backbone may contain comonomers,... 

When the two coordinating centres are not in separate ions but are joined by bridging groups, the isomers are often distinguished as coordination position isomers as is the case for ... 

The compounds are isolated by sublimation from the reaction mixture. Perhaps surprisingly the compounds fall into two quite distinct classes. Those of Np and Pu are unstable, volatile, monomeric liquids which at low temperatures crystallize with the 12-coordinate structure of Zr(BFl4)4 (Fig. 21.7, p. 969). The borohydrides of Th, Pa and U, on the other hand, are thermally more stable and less reactive solids. They possess a curious helical polymeric structure in which each An is surrounded by 6 BFI4 ions, 4 being bridging groups attached by 2 FI atoms and... 

The smooth intramolecular nucleophilic displacement of biphenyl carboxylic acids leading to benzocoumarins (See Section II.A.) inspired also investigation of the behavior of similar diphenyl ether, diphenyl sulfide and A-methyldiphenyl amine derivatives 458 under similar conditions. However, all these attempts to achieve cyclization to tricyclic compounds 459 were unsuccessful, probably due to the unfavorable stereochemistry for the formation of the required seven-mem-bered transition states and also to the presence of the deactivating bridge groups X (Eq. 42) [68JCS(C)1030]. 

The apparently loose structural requirements for antihista-iiiinic agents have already been alluded to. Thus, active compounds. ire obtained almost regardless of the nature of the atom that connects the side chain with the benzhydryl moiety. In fact, a methylene group, too, can also serve as the bridging group. Reaction of the aminoester, 95 (obtained by Michael addition of... 

Figure 20.3 Refrigerated LPG storage at Flotta. (Courtesy of the Motherwell Bridge Group)...

If a 2-naphthyl residue is bonded through a bridging group (X = CO, O, NCH3, or CH2) to the benzene ring, the naphthyl group may react at its 1- or 3-position... 

Scheme 10-78, Huisgen and Zahler, 1963 a, 1963 b). The yields and ratios of the two cyclization products 10.48 and 10.49 for the reagents with the four different bridging groups are given in Table 10-8. 

Diazo function Bridging group X Reaction conditions Yield 10.48 + 10.49 % Ratio 10.48 10.49... 

In nickel and palladium dithiobenzoato complexes, four-membered chelate rings are formed (366), whereas, in the corresponding phenyl-dithio acetates [M2(S2CCH2Ph)4], the dithio ligands act as bridging groups between the two metal atoms, with the formation of binuclear units (367). The molecular structure of the latter compounds shows that each metal atom is coordinated to four sulfur atoms and to the other metal atoms in a square-pyramidal geometry. Other evidence for... 

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