Carbon chains, abbreviations branched

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... 

Four types of organic amines exist, as shown in Table 4.8 primary amines RNHj, secondary R2NH2, tertiary RsNH, and quaternary R4N (Appendix D). The hydrocarbon chain R is usually of length Cg-Cu, commonly a straight aliphatic chain, but branched chains and aromatic parts also occur. In general the amines extract metal complexes in the order tertiary > secondary > primary. Only long-chain tertiary and—to a smaller extent—quarternary amines are used in industrial extraction, because of their suitable physical properties trioctylam-ine (TOA, 8 carbons per chain) and trilauryl amine (TLA, 12 carbons per chain) are the most frequently used. For simplicity we abbreviate all amines by RN, and their salts by RNH L . 

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. 

The butane with the unbranched carbon chain is called normal butane (abbreviated M-butane) it boils at 0.5°C and melts at -138.3 C. The branched-chain butane is called 2-methylpropane it boils at -11.7 C and melts at —159.5°C. These differences in physical properties are sufficient to establish that the two compounds, though they have the same molecular formula, are different substances. The structural arrangements of the atoms in methane, ethane, propane, butane, and 2-methylpropane are shown in Figure 19.4. 

FIGURE 9.1 GC/MS of total methyl esters of fatty acids standards and single fractions after PLC. Abbreviations first number (18 or 20) = number of carbon atoms in the chain second number (0 to 5) = number of double bounds n = normal chain i =isoacid ai = anteisoacid m-br =multi-branched acid. (From Rezanka, T., J. Chromatogr. A, 727, 147-152, 1996. With permission.)... 

Structural (or constitutional) isomers are compounds with the same molecular formulas but different structural formulas (that is, different arrangements of the atoms in the molecule). Isomerism is especially important in organic chemistry because of the capacity of carbon atoms to be arranged in so many different ways continuous chains, branched chains, and rings. Structural formulas can be written so that every bond is shown, or in various abbreviated forms. For example, the formula for n-pentane (n stands for normal) can be written as ... 

In the 0X0 industry, the term iso denotes a mixture of isomers and does not refer to the lUPAC definition. Therefore, the abbreviations included in Table 28.2 indicate when a phthalate ester is a mixture of branched or linear isomers (i.e., DNP for linear di-w-nonylphthalate, and DINP for branched diisononylphthalate). With the exception of di-(2-ethyUiexyl) phthalate, higher molecular weight phthalate esters (alkyl chains > 6 carbons) are mixtures based on the alcohols used for its production. Eor example, DINP is a mixture of di-C8-C10 branched alkylesters, containing principally isomers with nine carbon alkyl chains. In the same way, the term DIDP refers to a mixture of di-C9-ll branched alkyl esters (Cl0-rich) of phthalic acid. 

Notice how the propyl part of isopropyl still indicates three carbon atoms they are just joined together in a different way—in other words, as an isomer of the straight chain propyl group. Sometimes, to avoid confusion, the straight chain alkyl groups are called -alkyl (for example, -Pr, -Bu)—n for normal —to distinguish them from their branched counterparts. Iproniazid is an antidepressant drug with i-Pr in both structure and name. Isopropyl may be abbreviated to i-Pr, Pr, or Pr. We shall use the first in this book, but you may see the others used elsewhere. 

To save space, structural formulas are conveniently abbreviated as omdensed structural formulas such as CH3CH(CH3)CH(C2H5)CH2CH3 for 3-ethyl-2-methylpen-tane, where the CH3 (methyl) and C Hs (ethyl) groups are placed in parentheses to show that they are branches attached to the longest continuous chain of carbon atoms, which contains 5 carbon atoms. It is understood that each of the methyl and ethyl groups is attached to the carbon immediately preceding it in the condensed structural formula (methyl attached to the second carbon atom, ethyl to the third). 

Ethylhexyl- n An 8-carbon branched-chain radical of the formula C4H9CH(C2H5)CH2-, often called octyl in the plastics industry. For example, the common plasticizer di-2-ethylhexyl phthalate is commonly referred to as dioctyl phthalate and by its abbreviation, DOR... 

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