2, 2-Dimethyl-3-Pentanone

[Aleck Sun 1J]

In the organic textbook, question 2.27 asks to draw the structure for 2, 2-Dimethyl-3-Pentanone. I was wondering why the ketone doesn't get the lowest number when naming. When naming a parent chain, aren't we supposed to ensure that the lowest number goes to the functional groups before moving on to the carbons. In the review session, we learned that Rule 1 is the lowest # on suffix (aka functional group. Then Rule 2 is the lowest number on triple and double bonds. Finally we look at the carbon substituents for rule 3, but only if the first two rules don't apply. Could someone explain to me about the numbering for this molecule and why these rules don't seem to apply?

[Jonathan Zuo 2J]

For this particular molecule, no matter which terminal end of the 5 carbon chain you start counting on the ketone group will always be on the 3rd carbon. Because the ketone will always be on the third carbon, we start counting at the end that will give us the lowest numbering on our methyl groups, which is 2,2 instead of 4,4.