Imine vs Enamine - Online Tutor, Practice Problems & Exam Prep

Nucleophilic addition of amines to carbonyls produces imines and enamines. A primary amine reacts with a carbonyl to form an imine, characterized by a nitrogen double bond. In contrast, a secondary amine yields an enamine, where the double bond is adjacent to one of the R groups to avoid formal charges. Both mechanisms pass through an iminium cation intermediate. The steps include protonation, nucleophilic attack, proton transfer, and elimination for enamines, highlighting the importance of alpha hydrogen removal in the process.

General Reactions

In this next page, we're going to talk about the nucleophilic addition of neutral amines to carbonyls. This is going to yield imines and enamines. The difference between an imine and an enamine is simply going to be the type of amine that the carbonyl is reacting with. As you guys can see, when you react a carbonyl with a primary amine, you're going to get an imine. An imine has a functional group of basically a nitrogen with a double bond on it and possibly an R group on the top. Think about an imine as kind of like a carbonyl, but with a nitrogen. If you can think about it as if it would have been a carbonyl with an oxygen, then that's an imine with a nitrogen on it. Notice that when I react a secondary amine, I get a different looking compound. This amine has two R groups. Instead of getting the double bond directly on the end, I actually get it down towards one of the R groups.

We're going to go through both of these mechanisms completely. But I just want to ask you guys why do you think that double bond might move? Why do you think it might be towards the bottom? Because if you have two R groups on your end, that means that if I were to put the double bond on the end, I would get a formal charge. To eliminate the formal charge, I'm going to have to move the double bond down to one of the R groups. That's the biggest difference between an imine and an enamine. In fact, they're pretty much the same exact reaction except for the final step. What we're going to do is we're going to go through both of these mechanisms. I do want to say one thing really quick that both of these mechanisms are going to pass through a very important intermediate. That intermediate is called the iminium cation. The iminium cation looks like this: It's your nitrogen with a double bond and with two things on it, so either Hs or Rs and a plus charge. We're always going to pass through the iminium cation, and then how we resolve t

Enamine Mechanism

Enamines are created when a carbonyl—we're just going to take our simple ketone again, acetone—reacts with a secondary amine in the presence of acid. I'm going to use acid. It turns out that many of the secondary amines used for the enamine process are actually cyclic because if you put an N in a ring, it's a secondary. Let's use a cyclic secondary amine. These are very common in organic chemistry. A cyclic secondary amine, it could have not been but I'm just using it just because. Also, if you guys don't mind, let's go ahead and assume that my cyclic amine plus my proton is going to make the conjugate acid which looks like this. Oh wait, which looks like it has 2 H's. Cool.

In my first step, I'm going to take my protonated version or my acidic version of my amine and I'm going to protonate. What this is going to give me is a positively charged oxygen, which after you draw the resonance structure will have a highly electrophilic carbon. What happens now? You got it. Nucleoph

Here’s what students ask on this topic:

What is the difference between an imine and an enamine?

The difference between an imine and an enamine lies in the type of amine reacting with the carbonyl compound. An imine is formed when a carbonyl reacts with a primary amine, resulting in a nitrogen double-bonded to a carbon. In contrast, an enamine is produced when a carbonyl reacts with a secondary amine, where the double bond is adjacent to one of the R groups to avoid formal charges. Both reactions pass through an iminium cation intermediate, but the final step determines whether the product is an imine or an enamine.

How is an imine formed from a carbonyl compound?

An imine is formed when a carbonyl compound reacts with a primary amine in the presence of an acid catalyst. The mechanism involves several steps: protonation of the carbonyl oxygen, nucleophilic attack by the amine, proton transfer, and elimination of water to form the iminium cation. Finally, deprotonation of the iminium cation yields the imine, characterized by a nitrogen double-bonded to a carbon.

What is the role of the iminium cation in the formation of imines and enamines?

The iminium cation is a crucial intermediate in the formation of both imines and enamines. It is formed after the nucleophilic attack of the amine on the protonated carbonyl compound. The iminium cation has a positively charged nitrogen with a double bond. The resolution of this cation determines the final product: deprotonation of the iminium cation leads to the formation of an imine, while elimination of an alpha hydrogen leads to the formation of an enamine.

Why does the double bond in an enamine form adjacent to one of the R groups?

The double bond in an enamine forms adjacent to one of the R groups to avoid creating a formal charge on the nitrogen. In the mechanism, after the formation of the iminium cation, the nitrogen cannot be deprotonated because it has no hydrogen atoms. Instead, an alpha hydrogen (next to the carbonyl) is removed, resulting in the formation of a double bond adjacent to one of the R groups. This step is crucial to stabilize the molecule and avoid formal charges.

What are the steps involved in the formation of an enamine?

The formation of an enamine involves several steps: 1) Protonation of the carbonyl oxygen, 2) Nucleophilic attack by the secondary amine, 3) Proton transfer to form a good leaving group, 4) Elimination of water to form the iminium cation, and 5) Deprotonation of an alpha hydrogen to form the enamine. The final product is characterized by a nitrogen with a single bond and a double bond adjacent to one of the R groups.