Michael Addition - Online Tutor, Practice Problems & Exam Prep

The Michael reaction is a 1,4-conjugate addition involving an enone and an enolate, akin to a double aldol reaction. The product is a 1,5-dicarbonyl compound. The mechanism begins with the enolate attacking the electrophilic carbon of the enone, forming a new bond while breaking the pi bond. This results in a negatively charged intermediate that is protonated to yield an enol tautomer, which can tautomerize to the more stable keto form. Understanding this mechanism is crucial for grasping conjugate additions in organic synthesis.

General Reaction

In this video, we're going to focus on a specific form of conjugate addition to an enone called the Michael reaction. The Michael reaction is a 1,4-conjugate addition. Remember that when I say 1,4-conjugate addition, I'm talking about an enone. I'm talking about adding right there, of an enone with an enolate. Remember that specifically, if your nucleophile is an enolate, that is called a Michael reaction if that is your nucleophile. Basically, if you think about it, this is kind of like an aldol times 2 because your first aldol reaction created the enone. And now I'm doing a second aldol reaction. I like to think of a Michael reaction as an aldol times 2.

What's cool about these is that they're always going to form the same thing. They're always going to form 1,5-dicarbonyls. Let me show you guys how to draw the products first, and then I'll show you the whole mechanism. The products are really easy. In this situation, because we're doing a conjugate addition, my rules of where to line up your enolate and your electrophile for aldol go out the window. I don't want that anymore. What I prefer you to do is to draw the enone at the bottom exactly the way it is but without its double bond and then draw a single bond coming off of the conjugate position, so position 4. And then just draw that attached to your enolate. That's how you draw the product. It's literally enone, enolate, new bond. Then obviously, I pointed this out earlier, no pi bond. Don't draw a double bond there. What I like to do is, regardless of whatever the nucleophile is, I like to just draw it right on top.

But we have to go into the mechanism. In this next video, I'm going to show you the full mechanism for the Michael reaction. This is also going to help you guys understand why that pi bond isn't there because that could be a little confusing. Why is that pi bond gone? We're going to talk about it. That's coming up in the next video.

General Mechanism

All right, guys. Let's bring the molecule down and we're going to draw the full mechanism. Oops. Let me make sure I got it right. I've got this molecule and I've got my enolate. What's going to happen is that remember that I said I have 2 electrophilic regions. I have this electrophile here. We're used to seeing that. But this is also an electrophile now. It doesn't look like it because it's a double bond. But it is because it can resonate. That positive charge can resonate. In my first step, I actually get this kind of strange arrow of the negative attacking this carbon. If I make that bond, I have to break a bond. I'm going to break this bond and make a double bond here. I'm going to break this bond and make a lone pair there. What I'm going to get is something that looks like this. O negative, double bond, single bond. That single bond has a new bond that's attached to my old enolate. Is that making sense so far? I have a negative charge and I have a double bond. What's going to happen is that this molecule gets protonated because notice that we have an enolate. There must be some kind of conjugate that took off that H. Let's just say that it had been hydroxide, so we'll use water to protonate. Now we're going to protonate. We're going to protonate and that's going to give us a molecule that you should know something about. Let's draw it first. I have a molecule that's similar to my HC dicarbonyl, But what do we call this species down here? What is that? Do you recognize that that's a vinyl alcohol Or more specifically, this is an enol tautomer. That's an enol tautomer. Now this is in a basic environment. Through tautomerization, that double bond, that enal tautomer is going to switch to the keto form. Remember that the keto form is pretty much always the most stable unless it's a beta dicarbonyl. Through tautomerization, I'm going to regenerate the keto form and I'm going to get this. If you want more information on the tautomerization mechanism, definitely feel free to go through the tautomerization videos that I have and I explain everything there. But at this point of the course, you just need to be able to use tautomerization. You don't have to draw every time. That shows you the full mechanism for Michael reaction which this also applies to any conjugate addition. Just so you know, this mechanism, this is the same mechanism for any conjugate addition. Now you know what that looks like and we know how to make a HC dicarbonyl. Let's move on to the next video.

Determine the product in the following conjugated addition reaction. 

• A.
• B.
• C.
• D.

Determine the product in the following conjugated addition reaction. 

• A.
• B.
• C.
• D.

Determine the product in the following conjugated addition reaction

• A.
• B.
• C.
• D.

Here’s what students ask on this topic:

What is the Michael reaction in organic chemistry?

The Michael reaction is a type of 1,4-conjugate addition reaction in organic chemistry. It involves the addition of a nucleophile, typically an enolate, to an α,β-unsaturated carbonyl compound (enone). The reaction results in the formation of a 1,5-dicarbonyl compound. The mechanism starts with the enolate attacking the β-carbon of the enone, breaking the π-bond and forming a new C-C bond. This intermediate is then protonated to form an enol tautomer, which subsequently tautomerizes to the more stable keto form.

How do you draw the product of a Michael addition reaction?

To draw the product of a Michael addition reaction, follow these steps: First, draw the enone without its double bond. Then, draw a single bond extending from the β-carbon (position 4) of the enone. Attach the enolate to this single bond. The resulting structure will be a 1,5-dicarbonyl compound. Ensure that the double bond from the enone is not present in the final product, as it is broken during the reaction.

What is the mechanism of the Michael reaction?

The mechanism of the Michael reaction involves several steps: First, the enolate nucleophile attacks the β-carbon of the enone, breaking the π-bond and forming a new C-C bond. This creates a negatively charged intermediate. This intermediate is then protonated, typically by water, to form an enol tautomer. Finally, the enol tautomer undergoes tautomerization to convert into the more stable keto form, resulting in a 1,5-dicarbonyl compound.

What is the difference between a Michael addition and an aldol reaction?

While both the Michael addition and aldol reaction involve enolates, they differ in their mechanisms and products. The Michael addition is a 1,4-conjugate addition where an enolate adds to an α,β-unsaturated carbonyl compound, resulting in a 1,5-dicarbonyl compound. In contrast, the aldol reaction is a 1,2-addition where an enolate adds to an aldehyde or ketone, forming a β-hydroxy carbonyl compound. The Michael addition can be thought of as an aldol reaction followed by another aldol reaction, leading to a more extended carbon chain.

Why is the π-bond in the enone broken during the Michael reaction?

The π-bond in the enone is broken during the Michael reaction because the enolate nucleophile attacks the β-carbon of the enone. This attack forms a new C-C bond, which necessitates the breaking of the π-bond to accommodate the new bonding arrangement. The resulting intermediate has a negative charge that is stabilized through resonance, and this intermediate is then protonated to form the final product.