Alkyl groups, common

Some of the common aromatics found in crude oil are the simple derivatives of benzene in which one or more alkyl groups (CHg) are attached to the basic benzene molecule as a side chain which takes the place of a hydrogen atom. These arenes are either liquids or solids under standard conditions. 

Classical syntheses of steroids consist of the stepwise formation of the four rings with or without angular alkyl groups and the final construction of the C-17 side-chain. The most common reactions have been described in chapter 1, e.g. Diels-AIder (p. 85) and Michael additions (p. 

Branched alkyl groups are named by using the longest continuous chain that begins at the point of attachment as the base name Thus the systematic names of the two C3H7 alkyl groups are propyl and 1 methylethyl Both are better known by their common names n propyl and isopropyl respectively... 

A single alkane may have several different names a name may be a common name or it may be a systematic name developed by a well defined set of rules The most widely used system is lUPAC nomencla ture Table 2 6 summarizes the rules for alkanes and cycloalkanes Table 2 7 gives the rules for naming alkyl groups... 

The lUPAC rules permit cer tain common alkyl group names to be used These include n propyl isopropyl n butyl sec butyl isobutyl tert butyl and neopentyl (Section 2 13)... 

We noted m Section 2 13 that the common names of certain frequently encoun tered alkyl groups such as isopropyl and tert butyl are acceptable m the lUPAC sys tern Three alkenyl groups—vinyl, allyl, and isopropenyl—are treated the same way... 

Formic acid exhibits many of the typical chemical properties of the aHphatic carboxyHc acids, eg, esterification and amidation, but, as is common for the first member of an homologous series, there are distinctive differences in properties between formic acid and its higher homologues. The smaller inductive effect of hydrogen in comparison to an alkyl group leads, for example, to formic acid = 3.74) being a considerably stronger acid than acetic acid... 

Substituted heat-reactive resins are most widely used in contact-adhesive appHcations and, to a lesser extent, in coatings (77,78) -butylphenol, cresol, and nonylphenol are most frequendy used. The alkyl group increases compatibiHty with oleoresinous varnishes and alkyds. In combination with these resins, phenoHcs reduce water sensitivity. Common appHcations include baked-on and electrical insulation varnishes, and as modifiers for baking alkyds, rosin, and ester gum systems. Substituted heat-reactive resins are not used for air-dry coatings because of theh soft, tacky nature in the uncured state substituted nonheat-reactive phenoHcs are the modifying resin of choice in this case. 

Quaternary ammonium compounds are usually named as the substituted ammonium salt. The anion is Hsted last (3). Substituent names can be either common (stearyl) or lUPAC (octadecyl). If the long chain in the compound is from a natural mixture, the chain is named after that mixture, eg, taHowalkyL Prefixes such as di- and tri- are used if an alkyl group is repeated. Complex compounds usually have the substituents Hsted in alphabetical order. Some common quaternary ammonium compounds and their appHcations in patent Hterature are Hsted in Table 1. 

One example of substituent replacement involves cleavage of a highly branched alkyl group. The alkyl group is expelled as a carbocation, and for this reason, substitution is most common for branched alkyl groups. The nitration of l,4-bis(i-propyl)benzene provides an example ... 

When an alkyl group migrates, there is an additional stereochemical feature to consider. The shift can occur with retention or inversion at the migrating center. The analysis of sigmatropic shifts of alkyl groups is illustrated in Fig. 11.7. The allowed processes include the suprafacial 1,3-shift with inversion and the suprafacial 1,5-shift with retention. Sigmatropic rearrangements of order [3,3] are very common ... 

Primary halides are more reactive than secondary compounds quaternary salt formation does not occur with tertiary halides, elimination always occurring to give the hydriodide and an olefln, Also, the larger the alkyl group the slower is the reaction this is shown by the very slow reaction of dodecyl bromide with quinoline, and even butyl iodide is much slower to react than methyl iodide. The longer chain primary halides commonly undergo elimination rather than cause quaternization for example, n-octyl and cetyl iodides give only the hydriodides when heated with 9-aminoacridine. ... 

For historical reasons, some of the simpler branched-chain alkyl groups also have nonsystematic, common names, as noted earlier. 

The common names of these simple alkyl groups are so well entrenched in the chemical literature that IUPAC rules make allowance for them. Thus, the following compound is properly named either 4-(l-methvlethyl)heptane or 4-iso-propylheptane. There is no choice but to memorize these common names fortunately, there are only a few of them. 

Acyl phosphates are named by citing the acyl group and adding the word phosphate. Tf an alkyl group is attached to one of the phosphate oxygens, it is identified after the name of the acyl group. In biological chemistry, acyl adenosyl phosphates are particularly common. 

With most common monomers, the rate of the reverse reaction (depropagation) is negligible at typical polymerization temperatures. However, monomers with alkyl groups in the a-position have lower ceiling temperatures than monosubstituted monomers (Table 4.10). For MMA at temperatures <100 °C, the value of is <0.01 (Figure 4.4). AMS has a ceiling temperature of <30 °C and is not readily polymerizable by radical methods. This monomer can, however, be copolymerized successfully (Section 7.3.1.4). 

When enamines are treated with alkyl halides, an alkylation occurs that is analogous to the first step of 12-14. Hydrolysis of the imine salt gives a ketone. Since the enamine is normally formed from a ketone (16-12), the net result is alkylation of the ketone at the a position. The method, known as the Stork enamine reaction is an alternative to the ketone alkylation considered at 10-105. The Stork method has the advantage that it generally leads almost exclusively to monoalkylation of the ketone, while 10-105, when applied to ketones, is difficult to stop with the introduction of just one alkyl group. Alkylation usually takes place on the less substituted side of the original ketone. The most commonly used amines are the cyclic amines piperidine, morpholine, and pyrrolidine. 

A common feature of the reactions in this section is that they serve to introduce functionality at a position remote from functional groups already present. As such, they have proved very useful in synthesizing many compounds, especially in the steroid field (see also 19-2 and 19-14). When N-haloamines in which one alkyl group has a hydrogen in the 4 or 5 position are heated with sulfuric acid, pyrrolidines or piperidines are formed, in a reaction known as the Hofmann-Loffier reaction... 

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