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In
chemical nomenclature A chemical nomenclature is a set of rules to generate systematic names for chemical compounds. The nomenclature used most frequently worldwide is the one created and developed by the International Union of Pure and Applied Chemistry (IUPAC). Th ...
, nor- is a
prefix A prefix is an affix which is placed before the stem of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix ''un-'' is added to the word ''happy'', it creates the word ''unhappy''. Particul ...
to name a
structural analog A structural analog (analogue in modern traditional English; Commonwealth English), also known as a chemical analog or simply an analog, is a compound having a structure similar to that of another compound, but differing from it in respect to a c ...
that can be
derived Derive may refer to: *Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguation ...
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 , , or CH group, or of a C atom. The "nor-" prefix also includes the elimination of a methylene bridge in a
cyclic Cycle, cycles, or cyclic may refer to: Anthropology and social sciences * Cyclic history, a theory of history * Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr. * Social cycle, various cycles in so ...
parent compound, followed by
ring contraction Ring expansion and ring contraction reactions in the course of organic synthesis refer to a set of reactions which can lead to the expansion or contraction of an existing ring. This often makes it possible to access structures that would be diff ...
. (The prefix "homo-" which indicates the next higher member in a
homologous series In organic chemistry, a homologous series is a sequence of compounds with the same functional group and similar chemical properties in which the members of the series can be branched or unbranched, or differ by molecular formula of and mole ...
, is usually limited to noncyclic carbons).''Preferred IUPAC Names, Provisional Recommendation''
september 200
Chapter 1
13.4.4.3 By the prefix ‘nor’, pp.18-19
IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN)

Nomenclature of Retinoids, Recommendations 1981; 4.6.
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. 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 lettersPreferred IUPAC Names Provisional Recommendation, September 2004; Chapter 1, 16.5.3 Italic terms, pp.89-90 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). 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. 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.


History

Possibly the earliest known use of the
prefix A prefix is an affix which is placed before the stem of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix ''un-'' is added to the word ''happy'', it creates the word ''unhappy''. Particul ...
"nor" is that by A. Matthiessen and G.C. Foster in 1867 in a publication about the reaction between a strong acid and opianic acid (see picture).
Opianic acid (C10H10O5) is a compound with two methyl-groups and they called it "dimethyl nor-opianic acid". After reaction with a strong acid a compound was attained with only one methyl (C9H8O5). This partially demethylated opianic acid they called "methyl normal opianic acid". The completely demethylated compound (C8H6O5) was denoted by the term "normal opianic acid", abbreviated as "nor-opianic acid". Similarly Matthiessen and Foster called
narcotine Noscapine (also known as Narcotine, Nectodon, Nospen, Anarcotine and (archaic) Opiane) is a benzylisoquinoline alkaloid, of the phthalideisoquinoline structural subgroup, which has been isolated from numerous species of the family Papaveraceae ( ...
, which has three
methoxy In organic chemistry, a methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula . On a benzene ring, the Hammett equation classifies a methoxy substituent at the ''para'' position a ...
groups, "trimethyl nor-narcotine". The singular demethylated narcotine was called "dimethyl nor-narcotine", the more demethylated narcotine "methyl nor-narcotine" and the completely demethylated form "normal narcotine" or "nor-narcotine".A. Matthiessen and G.C. Foster: ''"Researches into the chemical constitution of narcotine and of its products of decomposition"''; J. Chem. Soc., 358 (1868). Abstract published in
''"Proceedings of the Royal Society of London, Volume 16"''
pp. 39-41. PDF

/ref> ''"Since that time the meaning of the prefix has been generalized to denote the replacement of one or more methyl groups by H, or the disappearance of CH2 from a carbon chain"''. At present, the meaning is restricted to denote the removal of only one group from the parent structure, rather than the completely demethylated form of the parent compound. In literature, "nor" is sometimes called the "next lower homologue", although in this context Homology (chemistry), "homologue" is an inexact term. "Nor" only refers to the removal of one carbon atom with the accompanying hydrogen, not the removal of other units. "Nor" compares two related compounds; it does not describe the relation to a
homologous series In organic chemistry, a homologous series is a sequence of compounds with the same functional group and similar chemical properties in which the members of the series can be branched or unbranched, or differ by molecular formula of and mole ...
.


False etymology

It is suggested that "nor" is an
acronym An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in ''NATO'' (''North Atlantic Treaty Organization''), but sometimes use syllables, as ...
of German "N ohne Radikal" ("
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
without
radical Radical may refer to: Politics and ideology Politics * Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe an ...
"). At first, the British pharmacologist John H. Gaddum followed this theory,(non-free access) but in response to a review of A.M. Woolman, Gaddum retracted his support for this etymology. Woolman believed that "N ohne Radikal" was a German
mnemonic A mnemonic ( ) device, or memory device, is any learning technique that aids information retention or retrieval (remembering) in the human memory for better understanding. Mnemonics make use of elaborative encoding, retrieval cues, and image ...
and likely a
backronym A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The ...
, rather than the real meaning of the prefix "nor". This can be argued with the fact ''"that the prefix nor is used for many compounds which contain no nitrogen at all"''.


Obsolete use of the term

Originally, "nor" had an ambiguous meaning, as the term "normal" could also refer to the unbranched form in a series of isomers, for example as with
alkanes In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in ...
, alkanols and some amino acids.''System of Nomenclature for TERPENE HYDROCARBONS''-Volume 14
American Chemical Society, (1955); Appendix D The Prefix Nor-;
IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN)

Nomenclature and Symbolism for Amino Acids and Peptides; 15.2.3.
IUPAC-IUB Commission on Biochemical Nomenclature (JCBN)
''Abbreviated designation of amino acid derivatives and peptides-Tentative rules''
The Journal of Biological Chemistry, Vol. 241, No. 11, Issue of June 10, 1966, p. 2492
Names of unbranched alkanes and alkanols, like " normal butane" and " normal propyl alcohol", which are obsolete now, have become the prefix ''n-'', however, not "nor". Other "normal" compounds got the prefix "nor". The IUPAC encourages that older
trivial name In chemistry, a trivial name is a non systematic name for a chemical substance. That is, the name is not recognized according to the rules of any formal system of chemical nomenclature such as IUPAC inorganic or IUPAC organic nomenclature. A ...
s, like norleucine and norvaline, not be used; the use of the prefix for isomeric compounds was already discouraged in 1955 or earlier.


Examples


See also

* Norsteroid


References

{{Orgchemsuffixes Chemistry prefixes