Ketone Naming Clarification

[BridgetJ_2J]

Just to clarify, for ketones with 4 or less carbons , numbering the position of the functional group isn't required ?

[Chem_Mod]

Ketones need a minimum of 3 carbons since you need a carbon on each side of the carbonyl. Therefore if it is a 3 carbon chain, the ketone will have to be in the middle. If you have a 4 carbon chain, the carbonyl can either be on the 2nd or 3rd carbon (if we count from the left). But if it is the 3rd carbon from the left, it is also the 2nd if we count from the right. So in order to get a lower number, you would need to number it from right to left.