Acyl Group vs. Carbonyl Group

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

There are several different types of groups in organic chemistry. In this lesson, we will learn about the acyl and carbonyl group, how they are related and how they are different.

Acyl and Carbonyl Relationship

What is the difference between dairy products and yogurt products? We know that all yogurt products are dairy products, but not all dairy products are yogurt products. In other words, yogurt is a subset of dairy. This is the same relationship between the acyl and carbonyl groups. The carbonyl group is the larger group (the dairy) and the acyl group is the subset (the yogurt).

Organic chemistry uses groupings such as the acyl and carbonyl groups based upon similar physical and chemical properties of compounds.

The Carbonyl Group

The carbonyl group is simply a carbon double bonded to an oxygen. The other two bonds on the carbon can be anything, from a hydrogen to a long, complicated carbon chain. It is important to note that the carbonyl group is ONLY the C=O bond. The carbonyl group does not include any of the other connections on the carbon.

The carbonyl group only includes the carbon to oxygen double bond
carbonyl group

The hybridization for the carbon and the oxygen are both sp2. Both the carbon and the oxygen have three hybrid sp2 surrounding them, one of these hybrid orbitals is shared between the oxygen and carbon. In the carbon, the other two hybrid orbitals can be bonded to anything else. In the oxygen, the other two hybrid orbitals each have a set of lone electrons. There is also a p orbital on the carbon and the oxygen, the p orbitals overlap, forming the double bond.

Since oxygen is much more electronegative than carbon, the electrons are slightly drawing towards the oxygen within the hybrid orbital. This puts a partial positive on the carbon atom and a partial negative on the oxygen atom. This also makes the carbon nucleophilic (electron loving, or needs electrons).

The Acyl Group

The acyl group is a specific type of a carbonyl group which includes one of the R groups connected to the carbonyl. The fourth bond is not part of the acyl group. Recall the dairy/yogurt comparison. With all dairy foods, all that we are concerned about is that there is dairy (milk) in the product. That is, we are only concerned about one ingredient. With yogurt, there needs to milk and bacteria cultures. Thus, we are concerned about 2 ingredients. It is the same with the acyl/carbonyl group. With the carbonyl group, we are only concerned with one bond, the C=O bond. With the acyl group, we are concerned with two bonds, the C=O bond and the C-R bond.

The acyl group includes the carbon to oxygen double bond and one of the other groups on the carbon
Acyl group

The 'R' can be any group. Typically the 'R' refers to a carbon chain, but it can also be another oxygen, a nitrogen or any other group.

The C=O bond is the same for the carbonyl and the acyl groups. They are both sp2 hybridized and the oxygen has a partial negative charge and the carbon has a partial positive charge.

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