Priorities side chains

If the same alkyl group occurs more than once as a side chain, this is indicated by the prefixes di-, tri-, tetra-, etc. Side chains are cited in alphabetical order (before insertion of any multiplying prefix). The name of a complex radical (side chain) is considered to begin with the first letter of its complete name. Where names of complex radicals are composed of identical words, priority for citation is given to that radical which contains the lowest-numbered locant at the first cited point of difference in the radical. If two or more side chains are in equivalent positions, the one to be assigned the lowest-numbered locant is that cited first in the name. The complete expression for the side chain may be enclosed in parentheses for clarity or the carbon atoms in side chains may be indicated by primed locants. 

Acyl Halides. Acyl halides, in which the hydroxyl portion of a carboxyl group is replaced by a halogen, are named by placing the name of the corresponding halide after that of the acyl radical. When another group is present that has priority for citation as principal group or when the acyl halide is attached to a side chain, the prefix haloformyl- is used as, for example, in fiuoro-formyl-. 

The sulfur atom in the -CH2SH group of cysteine makes the side chain higher in priority than the -C02H group. 

The functional group has priority in numbering over hydrocarbon side chains. 

The expected contribution of catalysis in this area will derive both from the availability, at low processing costs, of new monomers obtained from biomasses and from the development of an optimized combination of biotechnology processes with classical and new biocatalytic processes. Research priorities for catalysis in the area of polymers from renewable materials for packaging, furniture, domestic water purification and recycling include the need to develop novel catalysts, e.g., for functionalization of polymeric and dendrimeric materials, with side-chain photoactive molecular switches (to be used as smart materials), or the development of multifunctional materials, combining, for example, nanofiltration with catalytic reactivity. 

This L "amino acid" also has an R configuration because the -CH2Br side chain is higher in priority than the -CO2H group. 

Geometric isomerism is also possible in double-bonded carbon-heteroatom systems such as imines and oximes (CN), and in azo (NN) systems. For example, several cephalosporin derivatives contain an alkoxyimino side chain that may exist in or Z isomeric forms the azo compound prontosil may display similar isomerism (Fig. 14). A syn-anti system can also be applied to CN geometric isomers. In these cases, the priority assignments are made as described previously, and the isomer with highest priorities on the same face of the double bond are called syn, whereas those with these groups on opposite sides are named anti. 

Fig. 13.18. Stereochemical nomenclature for arylethanolamines versus aryloxypropanolamines. The relative positions in space of the four functional groups are the same in the two structures however, one Is designated (R) and the other (S). This Is because the introduction of an oxygen atom into the side chain of the aryloxypropanolamine changes the priority of two of the groups used in the nomenclature assignment.

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