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Offline anilin

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IUPAC name
« on: March 08, 2009, 08:39:45 AM »
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


Offline James Newby

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Re: IUPAC name
« Reply #1 on: March 08, 2009, 09:24:53 AM »
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!
4th year undergraduate at the University of Sheffield

Offline Vidya

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Re: IUPAC name
« Reply #2 on: March 08, 2009, 09:27:51 AM »
http://en.wikipedia.org/wiki/Piperidine

Check rules for IUPAC nomenclature of Hetrocyclic rings.
IUPAC nomenclature numbering is not based on alphabetical order.

Offline James Newby

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Re: IUPAC name
« Reply #3 on: March 08, 2009, 10:36:46 AM »
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.
4th year undergraduate at the University of Sheffield

Offline frenchy

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Re: IUPAC name
« Reply #4 on: March 08, 2009, 10:47:47 AM »
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
PhD student in synthetic Inorganic and Supramolecular chemistry.

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