Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: anilin on March 08, 2009, 08:39:45 AM
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Hi,
I have two questions:
1- Why the IUPAC name for Piperidine is Azacyclohexane? there is only 5 carbon in the ring, shouldn't it be azacyclopantane?
2- Re the IUPAC name for Pipecolic acid (1-azacyclohexane-2-carboxilic acid), the carboxyl groop is the main functional group. why is it given number 2 instead of 1?
thanks
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1, i think the Azacyclohexane means the nitrogen is encorperated in the count. If it was Azo it would be Azocyclopentane.
2, IUPAC name things in alphabetical order so A is before C, therefore the counting starts from the aza group instead of the carboxylic group.
Many people dislike the IUPAC system but its universal and likely to stay around for a while!
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http://en.wikipedia.org/wiki/Piperidine
Check rules for IUPAC nomenclature of Hetrocyclic rings.
IUPAC nomenclature numbering is not based on alphabetical order.
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sorry but IUPAC naming is alphabetically!
http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry#Cyclic_compounds
Quote:
Prefixed substituents are ordered alphabetically (excluding any modifiers such as di-, tri-, etc.), e.g. chlorofluoromethane, not fluorochloromethane. If there are multiple functional groups of the same type, either prefixed or suffixed, the position numbers are ordered numerically (thus ethane-1,2-diol, not ethane-2,1-diol.) The N position indicator for amines and amides comes before "1", e.g. CH3CH(CH3)CH2NH(CH3) is N,2-dimethylpropanamine.
I understand on carbon substituents (ie. alkyl chains) the numbering is based on the longest chain, and for heterocycles the numbering starts from the no carbon atom.
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I think as a general rule, the heterocycle being the "main component it takes priority. You always start numbering heterocycle by the "hetero atom" hence why your nitrogen is considered number 1 in both case