Chains, carbon atoms

The size of the group attached to the main chain carbon atom can influence the glass transition point. For example, in polytetrafluoroethylene, which differs from polyethylene in having fluorine instead of hydrogen atoms attached to the backbone, the size of the fluorine atoms requires the molecule to take up a twisted zigzag configuration with the fluorine atoms packed tightly around the chain. In this case steric factors affect the inherent flexibility of the chain. 

These polymers, typical of polyamides with fewer than four main chain carbon atoms in the repeating unit, decompose before melting and have to be processed from solution. Several of the polymers may, however, be spun into fibres. Over thirty years ago Courtaulds produced silk-like fibres on an experimental commercial scale from poly-(L-alanine) and from poly-(a-methyl-L-glutamate). The latter material is also said to be in use as a synthetic leather in Japan. The... 

Fig. 14 a, b. Two different and isosteric orientations of triplets of s-PS chains dark circles indicate the maih-chain carbon atoms. The presence of a statistical disorder of these orientations, in the positions indicated by large dashed circles in Fig. 7 a, characterize the disordered a modification [27, 9, 28]... 

In the n-butyl derivative 6, T, values of the side-chain carbon atoms... 

Polymers with chiral centres arising from rings linking adjacent main-chain carbon atoms can be included in this nomenclature ... 

CEJ1358> and the ruthenium mediated isomerization of double bonds (cf. Scheme 89, Section 8.11.7) <2007TL137> are recent examples of transition metal catalyzed manipulations at the side chain carbon atoms of 1,3-heterocycles. A novel side-chain addition reaction of aldehydes to 6-alkylidene-l,3-dioxin-4-ones was used for the construction of intermediates of lophotoxin <2006CJC1226>. An acid-catalyzed intramolecular cycloaddition of a hydroxy group to an alkene has been effected by the presence of an adjacent 1,3-dithiane moiety <2006TL4549>. 

Treatment of the reduced intermediate (23-6) with butyl hthium leads to the anion from the removal of a proton on the methylene group reaction of that with methyl acetate affords the methyl ketone (24-1), which contains two of the three required side chain carbon atoms. The additional carbon atom and the basic function are incorporated by means of a Mannich condensation. Thus, reaction of (24-1) with A-methylpiperazine and formaldehyde leads to the aminoketone (24-2). The carbonyl group is then reduced with sodium borohydride and the resulting alcohol is dehydrated by reaction with phosphoms oxychloride in pyridine. In this case, too, the Z isomer is responsible for most of the activity. This is isolated from the resulting mixture of olefins to afford thiothixene (24-3) [25]. 

N number of main-chain carbon atoms in polymer molecules. 

This fact might be attributed, in some cases, to the relatively low stereoregularity of the samples, and in general to the position of the asymmetric side chains carbon atom with respect to the principal chain. 

This method might be used to synthesize polymers containing in the principal chain carbon atoms, which are asymmetric owing to the differences in the chemical nature of the four groups directly bound to them... 

The methyl group in the y-position of the side-chain interferes with cyclization. The rate of C5-cyclization of n-butylbenzene at 371°C over platinum-on-silica gel is 3.5 times higher than that of 2-phenylpentane (Table IV) (14). The difference in C6-cyclization is even larger. Now, the side-chain carbon atoms involved in the cyclizations of n-butylbenzene and 2-phenylpentane have identical natures (i.e., secondary in five-membered ring closure and primary in six-membered ring closure). The difference between the two molecules (the extra methyl group) is far removed from the two carbon atoms involved in the formation of the new bond ... 

Outline of the biosynthesis of the 20 amino acids found in proteins. The de novo biosynthesis of amino acids starts with carbon compounds found in the central metabolic pathways. The central metabolic pathways are drawn in black, and the additional pathways are drawn in red. Some key intermediates are illustrated, and the number of steps in each pathway is indicated alongside the conversion arrow. All common amino acids are emphasized by boxes. Dashed arrows from pyruvate to both diaminopimelate and isoleucine reflect the fact that pyruvate contributes some of the side-chain carbon atoms for each of these amino acids. Note that lysine is unique in that two completely different pathways exist for its biosynthesis. The six amino acid families are screened. 

A different type of rearrangement in which the allyl group migrates to an open-chain carbon atom has been reported.26 Allyl ethers of the type XXIII with a propenyl group in the ortho position can be rearranged to phenols with the allyl group attached to the side chain XXIII yields XXIV in 37% yield when refluxed under diminished pressure at 177° for one hour. 

Considering the fine structure of cellulose, it is known that the majority, if not all, of the glucose units are linked by glycosidic combination into chains carbon atom 1 of one unit being linked to carbon atom 4 of the adjacent unit. Meyer s surmise37 that the copper enters into a complex with the hydroxyl groups on carbon atoms 2 and 3 of a single... 

Name the substituent groups attached to the longest chain as alkyl groups. Give the location of each alkyl group by the number of the main-chain carbon atom to which it is attached. 

Give position numbers to the carbon atoms in the parent chain. Attach all the branches to their appropriate parent chain carbon atoms. 

Attach all the branches to their appropriate parent chain carbon atoms. 

A simple, two-fold axis of symmetry (C2), and, hence, equivalence of the protons interchanged by this symmetry operation, is quite common in specific conformations of inositols and their derivatives, for example, the half-chair conformation (60) of myo-inosose-2 phe-nylosotriazole derivatives,187 and in derivatives of alditols having an even number of chain carbon atoms,188 for example, 2,3 4,5-dianhydro-D-iditol and its 1,6-diacetate and -benzoate189 (61). The 2,5-O-meth-... 

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