Acyl Group vs. Alkyl Group

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 difference between an acyl group and an alkyl group, what their structures are, and what specific aspects differentiate the two.

The Knight in Shining Armor

If a fight occurred between a knight, complete with full metal armor and weapons, and a regular man with no armor, who would win? Silly question, right? Clearly the knight with all of the armor would win. And really, all that differentiates the knight from the man is the armor. He's just a man with a little something extra.

It's the same thing with an acyl group and an alkyl group. The acyl group is just an alkyl group with a little something extra.

So What is an Alkyl Group Anyway?

To understand the difference between the two groups, let's start by looking at the alkyl group, the simpler of the two. An alkyl group is simply a part of a molecule that is made up of carbons and hydrogens. Keep in mind that it is not a molecule in and of itself, that would be called an alkane (a molecule made up of only carbons and hydrogens). An alkyl group is just a part of a molecule, made up of carbons and hydrogens, and it can have infinitely different structures. It can be just one carbon and its hydrogens, called a methyl group.


Methyl group


It can be two carbons, called an ethyl group.


Ethyl group


It can be a straight line of carbons, or it can be branched.


Isobutyl group


It can be cyclic or non-cyclic. It can contain as many carbons as you can imagine.

Then What is an Acyl Group?

Like we saw before, with the knight analogy, the acyl group has a little something extra. While an alkyl group is a part of a molecule made up of carbons and hydrogens, an acyl group has two parts. First, it has a carbonyl group. A carbonyl group is a carbon with a double bond to an oxygen. Second, it has an alkyl group. So as you can see, the acyl group is simply an alkyl group with a carbonyl group in front of it. This can take many forms, similar to the alkyl group. An acyl group that is made up of a carbonyl group and only one other carbon, a methyl group, is called an acetyl group.


Acetyl group


An acyl group made up of a carbonyl group and a benzene ring is called a benzoyl group.


Benzoyl group


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