[anilin]

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

[James Newby]

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!

[Vidya]

http://en.wikipedia.org/wiki/Piperidine

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

[James Newby]

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.

[frenchy]

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