numbering the carbons

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Fengting Liang 1F
Posts: 23
Joined: Sat Jul 09, 2016 3:00 am

numbering the carbons

Postby Fengting Liang 1F » Tue Mar 07, 2017 4:58 pm

Hi I was wondering, for a molecule like 1-ethyl-4-fluorocyclohexane, why couldn't it also be written as 4-ethyl-1-fluorocyclohexane?
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Fengting Liang 1F
Posts: 23
Joined: Sat Jul 09, 2016 3:00 am

Re: numbering the carbons

Postby Fengting Liang 1F » Tue Mar 07, 2017 5:00 pm

I guess what I'm trying to ask is, how do I know to start numbering the carbons at the one attached to the ethyl, and not the carbon that's attached to the fluorine?

Tiffany_Hoang_3C
Posts: 20
Joined: Wed Sep 21, 2016 2:59 pm

Re: numbering the carbons

Postby Tiffany_Hoang_3C » Tue Mar 07, 2017 5:28 pm

When the numbers are the same (1 and 4), the substituent that is named first (ethyl) should get the lower number (1).

samuelkharpatin2b
Posts: 55
Joined: Wed Sep 21, 2016 2:57 pm

Re: numbering the carbons

Postby samuelkharpatin2b » Wed Mar 08, 2017 5:45 pm

When naming, it is always best (if possible) for the substitutent "earlier" in alphabetical order to get the smaller number as well. Hence, ethyl would receive the number 1 and not 4.

angelicapayne
Posts: 10
Joined: Wed Sep 21, 2016 2:58 pm
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Re: numbering the carbons

Postby angelicapayne » Mon Mar 13, 2017 3:50 pm

Because alphabetically "e" comes before "f", you would want the ethyl to have the lowest number. When you start numbering at ethyl and go clockwise the fluoro is on the 4th carbon; similarly if you go counterclockwise the fluoro is still on the 4th carbon. (If these were different numbers, you would pick the direction that results in the lowest number) Therefore it is 1-ethyl-4-fluorocyclohexane


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