Building units chain

Figure 4.2 A number of secondary building units encountered in MOFs (a) the paddlewheel complex (b) the trioctahedral bipyramidal complex and (c) the infinite chain of octahedra. The squares and octahedra represent the metals within their...

Fig. 13.1 The structure of CS5I113AS4 contains both layers and chains of [InsAsJ shown in (a) and (b), respectively. Shown in boxes is the same building unit of the chains and the layers, i.e., a dimer of semicubanes of ln3As4.

A perspective view of this structure and a projection of the unit cell are shown in Fig. 4.36. Notice the chain structure resulting from the condensation of Ti6Te8 clusters. Similar groups (such as Mo6S8) are found, as building units, in several compounds. 

Figure 2.3 Some examples of chain composite building units, (a) Single chain (zig-zag) and (b) double chain (double zig-zag) with periodicities of two. (c) Single chain (crankshaft) and (d) double chain (double crankshaft) with periodicities of four, (e) Complex chain (designated mod by Smith...

Butyric acid is one of the simplest fatty acids. Fatty acids, which are the building units of fats and oils, are natural compounds of carbon chains with a carboxyl group (-COOH) at one end. Most natural fatty acids have an unbranched carbon chain and contain an even number of carbon atoms because during biosynthesis they are built in two carbon units from acetyl coenzyme A (CoA). Butyric acid is an unsaturated fatty acid, which means all carbon-carbon bonds are single bonds. Common names for fatty acids stem from their natural sources. In addition to butyric acid, some other common saturated fatty acids include lauric acid, palmitic acid, and stearic acid. Lauric acid was first discovered in Lauraceae (Laurus nobilis) seeds, palmitic oil was prepared from palm oil, and stearic acid was discovered in animal fat and gets its name from the Greek word stear for tallow. 

Building Hydrocarbon Chains with Two-Carbon Units... 

The synthesis of amino acids in which a nonfunctionalized alkyl group is covalently connected to the a-nitrogen has been discussed vide supra). In this section the synthesis of N-substituted amino acids in which the alkyl chain bears a protected functional group is discussed. The resulting amino acids have the general formula /Va-(m-functionalized alkyl) amino acids 28 (Scheme 17). These amino acids were developed for the solid-phase synthesis of backbone cyclic peptides 70 (see also Vol. E 22b, Section 6.8.3.2.4) [in this case they were called building units (BU)], for the synthesis of PNA 71 and for the synthesis of peptoids. 72 (In this case they were called monomers.)... 

This approach gave fair yields of Gly-based building units (R2=H). A similar approach was used 122 to prepare a variety of monomers (Scheme 18) used in the synthesis of Leu-enkephalin peptoids. In the case of substituted a-halocarboxylic acids or esters bearing R2 side chains the yields were lowered because of racemization and p-elimination resulting in the undesired a, 3-dehydrocarboxylic acids in addition to the desired chiral building unit. Another problem was polyalkylation. 

This procedure was improved 123 for the synthesis of building units based on amino acids other than Gly, but with nonfunctionalized side chains (Table 6). To suppress the 3-elim-ination and racemization side reactions, triflates of a-hydroxycarboxylic acid esters 124 34 (L = OTf, Scheme 19) were used as substrates for the nucleophilic substitution. In order to prevent polyalkylation, the nucleophilic amine of to-BocNH- or co-tBu02C-alkylamines 33 were temporarily protected with the benzyl group. 115116 This protection also improved the yields and purity of Gly-based building units. In this case commercially available benzyl bromoacetate 34 (L=Br) was used as the substrate. In both cases the nucleophilic sub-... 

An improved version of this procedure has been introduced 125 and used for the preparation of a large variety of Fmoc-protected Aa-(co-AlocNH-alkyl)- and N -(to-A102C-alkyl) amino acids 32 that contained sensitive, protected side chains. The to-protected functionalized aldehydes 41 and the zwitterionic amino acids 42 were dissolved in 1% AcOH/MeOH and then added to the mixture NaBH3CN in THF. After the completion of the reaction and removal of the solvents, the resulting unprotected A"-) to-protected functionalized alkyl) amino acids 43 were directly reacted with Fmoc-Cl to yield the Fmoc-protected building units 32. 

Fig. 19. The structure or ZSM-S/silicate (a) Secondary building units (indicated by bold lines) each composed of 12 tetrahedral atoms are linked into chains, one of which is shown in the c direction (b) The chains are interlinked to form a three-dimensional framework in which there are 10-membered ring openings (5.5 A in diameter) running in the [010] direction. In this portion of the ac structural projection, O denotes a tetrahedral site.

Pectins. The basic building unit of pectins is known to be a-1,4 linked D-galacturonic acid which forms the polygalacturonic acid chain. The carboxyl groups of the D-galacturonic acid in the chain are methylated to various degrees. 

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