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Nomenclature of Assemblies of Identical Units

Rule C-72. Assemblies Involving Bi- or Multi-valent Radicals

72.1 - When a compound contains identical units whose only substituents are the principal groups, and when these identical units are linked by a symmetrical bi- or multi-valent radical, it is named by stating successively (a) the locants for the positions of substitution of the radical into the units, (b) the name of the substituting radical, (c) the prefix "di" or "tri", etc., and (d) the name of the Unit including the principal groups. The numbering of the unit and the principal group is retained, and when there is a choice the points of substitution by the radical are numbered as low as permissible therewith. Primes, double primes, etc., are used to distinguish the locants, the highest receiving the largest number of primes.

Examples to Rule C-72.1

72.2 - Names of symmetrical compound radicals are formed by juxtaposing the names of the individual radicals starting with the central radical e.g., methylenedioxy, oxydiethylene; or the trivial name, if any, for the compound radical may be used.

Examples to Rule C-72.2

(In the last example the compound radical name is formed by starting with the central radical "oxy-", followed by "-bis-", and adding successively the names of the radicals "ethylene" (-CH2-CH2-) and "nitrilo" (-N=), and finally the name of the unit "propionic acid" is added.)

Note: On this nomenclature system, unsymmetrical compound radicals are not used for linking identical units because of difficulty in assigning unambiguous numbering to the complete structure. Instead, simple substitutive nomenclature is used, e.g.:

See Recommendations'93 R-2.4.4 and R-1.2.8

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Derivatives of Assemblies of Identical Units
Assemblies of Identical Acyclic Units

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This HTML reproduction of Sections A, B and C of IUPAC "Blue Book" is as close as possible to the published version [see Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F, and H, Pergamon Press, Oxford, 1979. Copyright 1979 IUPAC.] If you need to cite these rules please quote this reference as their source.

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