numbering the carbons

[Fengting Liang 1F]

Hi I was wondering, for a molecule like 1-ethyl-4-fluorocyclohexane, why couldn't it also be written as 4-ethyl-1-fluorocyclohexane?

[Fengting Liang 1F]

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]

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

[samuelkharpatin2b]

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]

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