ketone placement

[Diane_Zhao_3I]

Dr. Lavelle mentioned that aldehydes must be at the end of a carbon chain, but ketone can never be at the end. Can someone elaborate on why that is structurally?

[Meghna Patel 2L]

A ketone can never be at the end of a carbon chain because it is bonded to two carbons or two groups- so it might be somewhere in the middle of a carbon chain. You can't end a carbon chain with a C because it has to have 4 bonds. On the other hand, an aldehyde is bonded to one or two hydrogens; this means it can only go at the end of a carbon chain because the H will not have more than one bond- thus, ending the chain.