Sciencemadness Discussion Board

Nomenclature Positions

Schleimsäure - 24-5-2017 at 04:43

Can't find the right text passage. How was the numbering of postions in poly ring systems done again?

In 2,3,7,8-Tetrachlorodibenzodioxin the chlorines are in postions 2,3,7,8.

If one starts at the top Carbon of one benzene-ring I don't get how you come up with 7 and 8.

ImagesHandler.ashx.png - 5kB

It would be 2,3,9,10 if you go in a straight line.



Alice - 24-5-2017 at 04:58

This may help: http://www.acdlabs.com/iupac/nomenclature/79/r79_72.htm

Atoms being part of more than one cycle aren't counted (usually omitted, as you can see there is a way numbering them too).
Quote:
The system thus oriented is numbered in a clockwise direction commencing with the carbon atom not engaged in ring-fusion in the most counter-clockwise position of the uppermost ring, or if there is a choice, of the uppermost ring farthest to the right, and omitting atoms common to two or more rings.


[Edited on 24-5-2017 by Alice]

Schleimsäure - 24-5-2017 at 05:08

Thank you very much, that's it.

Alice - 24-5-2017 at 05:24

You're welcome. Nomenclature can be a real pain...

Schleimsäure - 24-5-2017 at 06:30

Quote: Originally posted by Alice  
You're welcome. Nomenclature can be a real pain...


Oh ja, especially if you're just an amateuer like me with an academic background in business admin;)
I watched some Organic Chemistry I and II on youtube from German Ruhr-University:
https://www.youtube.com/watch?v=HE6m7LYS3D4

The whole OC lecture there (over 100 lectures from Prof. Dyker).
Also shows how demanding a complete chemistry course is.




[Edited on 24-5-2017 by Schleimsäure]