What is Acetophenone? - Structure & Derivatives

Instructor: Laura Foist

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

In this lesson, we will look at the structure of Acetophenone. We will learn how the ketone on Acetophenone affects the reactivity of benzene. We will examine what types of derivatives can be obtained from acetophenone.

Structure

What does an orange, chicory, and some Parkinson drugs have in common? They all contain the compound Acetophenone. Acetophenone is the simplest ketone derivative of benzene. It is naturally found in several fruits and chicory. It has a distinctive orange scent. Thus it is often used in scenting lotions and flavoring food.

The name 'acetophenone' does not follow conventional IUPAC naming methods, because it is such a simple ketone it is known by the common name of acetophenone. The actual IUPAC name would be: 1-phenylethanone.

Looking at the name 1-phenylethanone we can actually derive the structure. We know that 'phenyl' refers to a benzene ring. The 'ethan' refers to the longest carbon chain having 2 carbon atoms. And the 'one' refers to a ketone. So let's start drawing this compound, let's start with the carbon chain, ethane:

Ethane

We know that at carbon 1 there is a benzene ring (the 1- before phenyl tells us that the phenyl group is at carbon 1):

Ethyl Benzene

And we know that it is a ketone:

Acetophenone

There are two reasons that we know the ketone needs to be on the first carbon.

  • If it was on the second carbon it would be an aldehyde instead of a ketone
  • Since the base name uses ethanone instead of ethane we know that the parent chain uses the ketone as the starting point, so we start counting at the ketone, in order to put it on the first possible carbon.

So we end up with the structure of acetophenone.

Benzene Derivative

Benzene is an aromatic compound, so it is a ring that shares pi-electrons along the entire ring. Since the pi-electrons (from the double bonds) are shared in the entire ring it is often drawn with dashed lines through the entire ring instead of with double bonds:

Benzene ring

When something reacts with benzene this continual electron sharing system is momentarily broken during the reaction. Benzene doesn't like to lose its aromaticity even for a little while, so it is difficult to react something with benzene.

With Acetophenone the ketone on benzene helps to activate the ring by sharing a partial positive charge through resonance so that the benzene ring can still keep its aromaticity for most of the reaction.

Resonance creating positive on benzene

Specifically the ketone is able to activate the ring when something is added in the para and ortho positions (because this is where the positive charge resonates onto). If we try to add something to the meta position then the ketone can't help share the positive charge, so it doesn't help benzene keeps its aromaticity.

Tomatoes contain a derivative of acetophenone which utilizes the ability for acetophenone to add an alcohol substituent in the ortho position:

2-hydrozyacetophenone

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