Lengthening carbon chain

All the normal acids show practically the same value of jB at a water-air interface, a value which gives the mean area per molecule of 24-3 0 3 Jl. This value is also given by i-butyric acid at a water-benzene interface. The values of B for the iso-acids are consistently a little larger than those for the normal acids. The values of x show that these acids resemble gases whose critical temperatures increase as the carbon chain lengthens. The iso-... 

If the alkyl halide is reacted with lithiomethyl phenyl tellurium in place of benzenetellurola-te, the alkyl halide is converted to an alkyl ether with the carbon chain lengthened by a methylene group. 

Inhibition by the aminooxy acids increased as the carbon chain lengthened from 1 to 4 (acetate to the butyrate) but then decreased as the length increased to 5 with the valerate. This is perhaps to be expected since the butyrate most closely resembles GABA, the substrate. 

Figure 13.27. Metabolic reactions involving acyl-CoA intermediates of xenobiotic acids, namely conjugations and two-carbon chain lengthening or shortening. Other products of /3-oxidation are shown in Fig. 13.30.

Examples of carbon chain lengthening by enol ether condensation are summarized in Tables 1 to 4. As interesting and useful results have also been achieved in another connection, the choice of reactions listed has not been limited strictly to the chemistry of polyenes and carotenoids. The reactions in the Tables are listed according to the increasing number of carbon atoms of the target compound. 

Focusing on completion of the synthesis, we examined one-carbon chain lengthening strategies based on masked acyl cyanides and on modified Petersen olefinations. Preliminary experiments were not promising, and we considered the modification of our scheme in order to bypass the need for homologation. 

In Summary Sugars can be made from other sugars by step-by-step one-carbon chain lengthening (cyanohydrin formation and reduction) or shortening (Ruff degradation). 

In Summary Step-by-step one-carbon chain lengthening or shortening, in conjunction with the symmetry properties of the various aldaric acids, allows the stereochemical assignments of the aldoses. 

Unsaturated Hydrocarbons. Olefins from ethylene through octene have been converted into esters via acid-catalyzed nucleophilic addition. With ethylene and propjiene, only a single ester is produced using acetic acid, ethyl acetate and isopropyl acetate, respectively. With the butylenes, two products are possible j -butyl esters result from 1- and 2-butylenes, whereas tert-huty esters are obtained from isobutjiene. The C5 olefins give rise to three j iC-amyl esters and one /-amyl ester. As the carbon chain is lengthened, the reactivity of the olefin with organic acids increases. 

The nib o-aldol reaction using l,l-diethoxy-2-nib oethane is useful for lengthening of the carbon chain of carbohydrates. The reaction of Eq. 3.86 proceeds in a stereoselective way (ds 75%) to give the syn-niho alcohol in 58% isolated yield.The product is converted into 2-amino-2-deoxyaldoses by reaction with Ha/Raney Ni. 

One of the oldest and best known carbonyl alkylation reactions is the malonic ester synthesis, a method for preparing a carboxylic add from an alkyl halide while lengthening the carbon chain by two atoms. 

Like nitromethane, 2-nitroethanol can be used as the methylene component for addition to aldehydes, giving epimeric nitrodiols in which the carbon chains have been lengthened by two carbon atoms. This reaction has attained preparative importance for the S5mthesis of higher-carbon ketoses 43,44) heptulose-phosphates 5) and of chloramphenicol... 

With a four-carbon chain either a CHjCHj or two CH, s must be added as branches to give a total of 6 C s. Placing CHXH, anywhere on the chain is ruled out because it lengthens the chain. Two CH, s are added, but only to central Cs to avoid extending the chain. If both CH, s are introduced on the same C, the isomer is... 

EXTENSIONS AND EXTRAPOLATIONS The loss of activity on lengthening the carbon chain on the meta-oxygen from two to three (from metaescaline to metaproscaline) discouraged any further exploration at this specific point of the molecule. The isopropyl analog (3,4-dimethoxy-5-(i)-propoxyphenethylamine, metaisoproscaline, MIP) was started and carried along as far as the aldehyde, and abandoned with the discovery that metaproscaline was without activity. There were other fish to fry. 

By how many carbon atoms is the chain lengthened Tips... 

Only one, six-carbon unit for chain lengthening has been studied. This is E-(N-2,5-hexadienyl)piperidine, prepared as described earlier in this chapter. This compound reacts with bromobenzene to give a 55% yield of the 6-phenyl derivative (8). The reaction with Z-... 

Alkanes are almost totally insoluble in water. They are soluble in benzene, carbon tetrachloride, chloroform, and other hydrocarbons. If an alkane contains a polar functional group, the polarity of the entire molecule, and thus its solubility, decreases as tlie carbon chain is lengthened. 

The Kiliani-Fischer synthesis lengthens the carbon chain of an aldose by one carbon at the aldehyde end and forms a new aldose with its corresponding epimers. When glucose and its epimer are produced from the corresponding pentose via the Kiliani-Fischer synthesis, and then both epimers are reacted with dilute nitric acid, both form optically active compounds. 

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