Chain carbons

In the longer carbon chains, two double carbon-carbon bonds may exist. Such molecules are called diolefins (or dienes), such as butadiene CH2 = CH - CH = CHj. 

Success of depositing compounds where an 18-carbon chain was attached to one end of an azobenzene group and various different hydrophilic groups attached to the other end has been reported in X and Z mode [52] and piezo-and pyroelectric effects were demonstrated. 

Most high polymeric substances are composed of carbon chains, but a few contain other elements, and one very important class will now be considered. 

It will be observed that the length of the carbon chain is increased by one carbon atom. 

The success of the last reaction depends upon the inertness of the ester carbonyl groups towards the organocadmium compound with its aid and the use of various ester acid chlorides, a carbon chain can be built up to any reasonable length whilst retaining a reactive functional group (the ester group) at one end of the chain. Experimental details are given for l-chloro-2-hexanone and propiophenone. The complete reaction (formation of ketones or keto-esters) can be carried out in one flask without isolation of intermediates, so that the preparation is really equivalent to one step. 

The lower members of other homologous series of oxygen compounds— the acids, aldehydes, ketones, anhydrides, ethers and esters—have approximately the same limits of solubility as the alcohols and substitution and branching of the carbon chain has a similar influence. For the amines (primary, secondary and tertiary), the limit of solubility is about C whilst for the amides and nitriles it is about C4. 

Another of Kelule s revelations that supposedly came to him in a dream was his famous structure of benzene. This related to how a carbon chain can close into a ring. To satisfy the four valenee of carbon, this, of course, raised the need to involve alternating double bonds. 

Any heteroatom (usually O, N, or S) in a carbon chain is a good point for a disconnection and I shall write CO, CN, or CS above the arrow when I use these disconnections. TM 234 can be made this way. How would you actually do it ... 

The last isomerization is remarkable in that the triple bond can shift through a long carbon chain to the terminus, where it is fixed as the (kinetically) stable acetylide. The reagent is a solution of potassium diami no-propyl amide in 1,3-di-aminopropane. In some cases alkali metal amides in liquid ammonia car also bring about "contra-thermodynamic" isomerizations the reactions are successful only if the triple bond is in the 2-position. 

In readily available (see p. 22f.) cyclic imidoesters (e.g. 2-oxazolines) the ot-carbon atom, is metallated by LDA or butyllithium. The heterocycle may be regarded as a masked formyl or carboxyl group (see p. 22f.), and the alkyl substituent represents the carbon chain. The lithium ion is mainly localized on the nitrogen. Suitable chiral oxazolines form chiral chelates with the lithium ion, which are stable at —78°C (A.I. Meyers, 1976 see p. 22f.). 

Heterocyde syntheses are often possible from difunctional open-chain precursors, including olefins as 1,2-difunctional reagents, and an appropiate nucleophile or electrophile containing one or more hetero atoms. The choice of the open-chain precursor is usually dictated by the longest carbon chain within the heterocyde to be synthesized. 

The longest carbon chain within a heterocycle indicates possible open-chain precursors. We use this chain as a basis to classify heterocycles as 1,2- to 1,6-difunctional systems. 

The synthesis of 11-oxaprostaglandlns from o-glucose uses the typical reactions of gl cofuranose diacetonide outlined on p. 267. Reduction of the hemiacetal group is achieved a thioacetal. The carbon chains are introduced by Wittig reactions on the aldehyde grou] which are liberated by periodate oxidation and laaone reduction (S. Hanessian, 1979 G Lourens, 1975). 

Cyclopentene derivatives with carboxylic acid side-chains can be stereoselectively hydroxy-lated by the iodolactonization procedure (E.J. Corey, 1969, 1970). To the trisubstituted cyclopentene described on p. 210 a large iodine cation is added stereoselectively to the less hindered -side of the 9,10 double bond. Lactone formation occurs on the intermediate iod-onium ion specifically at C-9ot. Later the iodine is reductively removed with tri-n-butyltin hydride. The cyclopentane ring now bears all oxygen and carbon substituents in the right stereochemistry, and the carbon chains can be built starting from the C-8 and C-12 substit""" ... 

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... 

Three isomeric alkanes have the molecular formula C5H12 The unbranched isomer is as we have seen n pentane The isomer with a single methyl branch is called isopen tane The third isomer has a three carbon chain with two methyl branches It is called neopentane... 

Pick out the longest continuous carbon chain and find the lUPAC name m Table 2 2 that corresponds to the unbranched alkane having that number of carbons This is the parent alkane from which the lUPAC name is to be derived... 

The same sequence of four steps gives the lUPAC name for the isomer that has Its methyl group attached to the middle carbon of the five carbon chain... 

Both remaining CgHi4 isomers have two methyl groups as substituents on a four carbon chain Thus the parent chain is butane When the same substituent appears more than once use the multiplying prefixes di tri tetra and so on A separate locant is used for each substituent and the locants are separated from each other by commas and from the words by hyphens... 

Higher alkanes having unbranched carbon chains are like butane most stable m then-all anti conformations The energy difference between gauche and anti conformations is similar to that of butane and appreciable quantities of the gauche conformation are pres ent m liquid alkanes at 25°C In depicting the conformations of higher alkanes it is often more helpful to look at them from the side rather than end on as m a Newman projec tion Viewed from this perspective the most stable conformations of pentane and hexane... 

Section 3 3 Higher alkanes adopt a zigzag conformation of the carbon chain m which all the bonds are staggered... 

Substitutive nomenclature of alkyl halides treats the halogen as a halo—(fluoro chloro bromo or lodo ) substituent on an alkane chain The carbon chain is numbered m the direction that gives the substituted carbon the lower number... 

When the carbon chain bears both a halogen and an alkyl substituent the two are con sidered of equal rank and the chain is numbered so as to give the lower number to the substituent nearer the end of the chain... 

Hydroxyl groups take precedence over ( outrank ) alkyl groups and halogen substituents m determining the direction m which a carbon chain is numbered The OH group is assumed to be attached to C 1 of a cyclic alcohol and is not numbered... 

---