Subtractive Nomenclature

Rule C-41

41.1 - The prefix "de-" (not "des-"), followed by the name of a group or atom (other than hydrogen), denotes replacement of that group or atom by hydrogen.

Example to Rule C-41.1

41.2 - Loss of two hydrogen atoms from a compound designated by a trivial name is denoted by a prefix "didehydro-".

Example to Rule C-41.2

Note: In common usage "dehydro-" is often used in place of "didehydro-". For example the above compound is often termed dehydrocholesterol; another such example is dehydroascorbic acid, where "dehydro" denotes loss of hydrogen from two hydroxyl groups in the conversion of HO-C=C-OH into CO-CO at positions 2 and 3:

41.3 - As an exception, "deoxy-", when applied to hydroxy compounds, denotes replacement of a hydroxyl group by a hydrogen atom.

Example to Rule C-41.3

See Recommendations'93 R-1.2.5

Subtractive Nomenclature
Rule C-42
Rule C-43
Rule C-44


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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