 So what you can see that I have here is a molecule with three carbons, one, two and three, and an oxygen that's attached to the end carbon, the number one carbon, with a double bond. So this is slightly different to what we've looked at before when we were looking at our hydroxyl groups. Now we're looking at an oxy group and that is double bonded to one of our carbons. Now the reason that we put the two groups of aldehydes and ketones together is because they are both characterized by the double bonded oxygen, but the place of that oxygen differs. And that's how we tell the difference between an aldehyde and a ketone.ropanel does not need a number. The reason that it does not need a number is because if we switch this to the other end and the simplest way for me to do that is just to rotate the molecule. Now it's on the opposite end. And so you can see it hasn't changed its position. There's no one propanel or propanel one L. That's, there's no need for us to number this.