Branched carbon chains

Methane is the only alkane of molecular formula CH4 ethane the only one that is C2H6 and propane the only one that is C3Hj Beginning with C4H10 however constitutional isomers (Section 1 8) are possible two alkanes have this particular molecular formula In one called n butane, four carbons are joined m a continuous chain The nmn butane stands for normal and means that the carbon chain is unbranched The second isomer has a branched carbon chain and is called isobutane... 

Butene has an unbranched carbon chain with a double bond between C 1 and C 2 It IS a constitutional isomer of the other three Similarly 2 methylpropene with a branched carbon chain is a constitutional isomer of the other three... 

The Prelog-Djerassi lactone (abbreviated here as P-D lactone) was originally isolated as a degradation product during structural investigations of antibiotics. Its open-chain equivalent 3 is typical of the methyl-branched carbon chains that occur frequently in macrolide and polyether antibiotics. The compound serves as a test case for the development of methods of control of stereochemistry in such polymethylated structures. There have been more than 20 different syntheses of P-D lactone.24 We focus here on some of those that provide enantiomerically pure product, as they illustrate several of the methods for enantioselective synthesis.25... 

The Prelog-Djerassi lactone (abbreviated as P-D-lactone) was originally isolated as a degradation product during structural investigation of antibiotics. Its open-chain precursor 1, is typical of methyl-branched carbon chains that occur frequently in macrolide and polyether antibiotics. 

PARAFFIN. (1) Also called alkane. A class of aliphatic hydrocarbons characterized by a straight or branched carbon chain generic formula CBH2n+2- Their physical form varies with increasing molecular weight from gases (methane) to waxy solids. They occur principally in Pennsylvania and mid-continent petroleum. (2) Paraffin Wax. 

As stated above, intermolecular coupling reactions between carbon atoms are of limited use. In the classical Wurtz reaction two identical primary alkyl iodide molecules are reduced by sodium. n-Hectane (C100H202), for example, has been made by this method in 60% yield (G. Stallberg, 1956). The unsymmetrical coupling of two alkyl halides can be achieved via dialkylcuprates. The first halide, which may have a branched carbon chain, is lithiated and allowed to react with copper(I) salts. The resulting dialkylcuprate can then be coupled with alkyl or aryl iodides or bromides. Although the reaction probably involves radicals it is quite stereoselective and leads to inversion of chiral halides. For example, lithium diphenyl-cuprate reacts with (R)-2-bromobutane with 90% stereoselectivity to form (S)-2-phenylbutane (G.M. Whitesides, 1969). 

Suresh et al. investigated the extraction of uranium and thorium by TsBP and TiBP (isomers of TBP with branched carbon chain) as an alternative choice for TBP (47). Higher homologues of TBP, for example, THP and TEHP, were reported to have higher extraction ability with reduced tendency toward third-phase formation (50, 51). The esters with bulkier substituents in place of the butyl group were proposed to be of practical value for the process applications in uranium and thorium separation (54). The LOC of thorium in equilibrium with aqueous nitric acid-thorium nitrate was reported to decrease in the order THP > TAP > TBP. Pathak et al. showed that TEHP can be a better choice for U/Th separation compared to TBP and TsBP (55). 

Just like some short straight carbon chains, some short branched carbon chains are given names and organic element symbols, The most common is the isopropyl group. Lithium diisopropylamide (also called LDA) is a strong base commonly used in organic synthesis. 

Pfibram and Handl found that when viscosities at one temperature are compared, they often differ for isomeric substances those of normal esters are greater than those of isomeric esters with branched carbon chains the viscosity is increased by substitution of halogen or NO2 for hydrogen, and in aromatic compounds it is influenced by the nature and position of the substituent. Cauquil found the viscosities of trans- greater than those of cw-isomers. Schulz reviewed the relation between viscosity and constitution. 

Humans cannot synthesize the branched carbon chains found in branched chain amino acids or the ring systems found in phenylalanine and the aromatic amino acids nor can we incorporate sulfur into covalently bonded structures. 

The presence of a methyl group and of a branched, carbon chain in o -D-glucosaccharinic acid was established by Krliani. Oxidation of o -D-glucosaccharinic lactone with silver oxide gave a mixture of acids... 

Isoalkanes are hydrocarbons containing branched carbon chains. They are also a major group of constituents of oil. Five most abundant and important oil isoprenoid compounds are farnesane (/-C15 2, 6, 10-trimethyl-dodecane), trimethyl-tridecane (i-Cig), norpristane (i-Cig 2, 6, 10-trimethyl-pentadecane), pristane (i-Cig 2, 6, 10, 14-tetramethyl-pentadecane) and phytane (i-C2o 2, 6, 10, 14-tetramethyl-hexadecane). 

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