Acetyl Group vs. Ketone

Instructor: David Jones

David has taught General and Organic Chemistry and has a master's degree in Chemistry.

In this lesson, you will learn the similarities and differences between an acetyl group and a ketone. We will also compare and contrast the structures of each.

A Piece of Cake

Who doesn't love cake? It's delicious! And we all know that the corner piece of cake is not the entire cake itself, and we all know that the icing is not the cake itself. We also know that icing isn't necessarily just on the corner piece, but is also on the other pieces. But what does that matter?

Moiety, Moiety, Moiety (try saying that five times fast!)

Well, comparing an acetyl group and a ketone is just like a piece of cake. Let's call the acetyl group the icing, and the ketone a corner piece. Neither one is the cake itself, just like neither the acetyl group nor the ketone are a molecule unto themselves—they are simply parts of molecules. A part of a molecule is called a moiety, so both an acetyl group and a ketone are a moiety.

Also, while the corner piece can sometimes have an icing as part of it, it doesn't have to (although how good is a cake without icing?). Likewise, the ketone can be made up in part by an acetyl group, but it certainly does not have to be.

So What is an Acetyl Group Anyway?

An acetyl group is made up of two parts. The first part is a carbonyl group, which is a carbon double bonded to an oxygen.

A Carbonyl Group

On one side of the carbonyl is the second part, called a methyl group, which is one carbon with its three hydrogens.

A Methyl Group
Methyl group

On the other side of the carbonyl is where the rest of the molecule is attached (remember that an acetyl group is a moiety, only part of a molecule, so the rest of the molecule attaches here). So when we combine the carbonyl, the methyl group, and a spot for the rest of the molecule, we get the structure of the acetyl group.

An Acetyl Group
Acetyl group

So What is a Ketone Anyway?

A ketone has three parts. The first part is a carbonyl, just like the acetyl group. However, the ketone has a requirement for both sides of the carbonyl. On each side of the carbonyl group must be a carbon atom. It doesn't matter what is attached to those carbon atoms as long as they are there. These carbon groups are often represented by the symbol 'R'.

A Ketone

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