 If I want to turn propanol into propanone, which is the correct name for the corresponding ketone, then all I'm gonna do is switch one of these carbons from one end to the other, which now means that my double bonded oxygen is on the central carbon. It's not on an end carbon, okay? We can have seven of these in a row, and it can be on the two, three, four, five, or six carbon as long as it's not on either end. One or seven, then you're going to have a ketone.