Nor-

In chemical nomenclature, nor- is a prefix to name a structural analog that can be derived from a parent compound by the removal of one carbon atom along with the accompanying hydrogen atoms. The nor-compound can be derived by removal of a CH
3, CH
2, or CH group, or of a C atom. The "nor-" prefix also includes the elimination of a methylene bridge in a cyclic parent compound, followed by ring contraction. (The prefix "homo-" which indicates the next higher member in a homologous series, is usually limited to noncyclic carbons).[1][2][3] The terms desmethyl- or demethyl- are synonyms of "nor-".

"Nor" is an abbreviation of normal. Originally, the term was used to denote the completely demethylated form of the parent compound.[4] Later, the meaning was restricted to the removal of one group. Nor is written directly in front of the stem name, without a hyphen between, unless there is another prefix after nor (for example α-). If multiple groups are eliminated the prefix dinor, trinor, tetranor, etcetera is used. The prefix is preceded by the position number (locant) of the carbon atoms that disappear (for example 2,3-dinor). The original numbering of the parent compound is retained. According to IUPAC nomenclature, this prefix is not written with italic letters[5] and unlike nor, when it is a di or higher nor, at the end of the numbers separated by commas, a hyphen is used (as for example 2,3-dinor-6-keto Prostaglandin F1α is produced by beta oxidation of the parent compound 6-keto Prostaglandin F1α).[6] Here, though, carbon 1 and 2 are lost by oxidation. The new carbon 1 has now become a CCOH similar to the parent compound, looking as if just carbon 2 and 3 have been removed from the parent compound. "Dinor" does not have to be reduction in adjacent carbons, e.g. 5-Acetyl-4,18-dinor-retinoic acid, where 4 referred to a ring carbon and 18 referred to a methyl group on the 5th carbon on the ring.[3]

The alternative use of "nor" in naming the unbranched form of a compound within a series of isomers (also referred to as "normal") is obsolete and not allowed in IUPAC names.

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "nor". doi:10.1351/goldbook.N04210
  2. ^ Preferred IUPAC Names, Provisional Recommendation september 2004 Chapter 1 13.4.4.3 By the prefix ‘nor’, pp.18-19
  3. ^ a b IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN): Nor Retinoids Nomenclature of Retinoids, Recommendations 1981; 4.6.
  4. ^ Cite error: The named reference gaddum-apology was invoked but never defined (see the help page).
  5. ^ Preferred IUPAC Names Provisional Recommendation, September 2004; Chapter 1, 16.5.3 Italic terms, pp.89-90
  6. ^ "2,3-dinor-6-keto Prostaglandin F1α (sodium salt) | Cayman Chemical".