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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: anilin on March 08, 2009, 08:39:45 AM

Title: IUPAC name
Post by: anilin on March 08, 2009, 08:39:45 AM
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?

Title: Re: IUPAC name
Post by: James Newby 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!
Title: Re: IUPAC name
Post by: Vidya on March 08, 2009, 09:27:51 AM

Check rules for IUPAC nomenclature of Hetrocyclic rings.
IUPAC nomenclature numbering is not based on alphabetical order.
Title: Re: IUPAC name
Post by: James Newby on March 08, 2009, 10:36:46 AM
sorry but IUPAC naming is alphabetically!


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.
Title: Re: IUPAC name
Post by: frenchy 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