What is the mechanism for this reaction? #learning #chemistry

Added: 2026-05-18

[00:00:00]What is a major product that is formed when we react with this alkene with H3PO4?

[00:00:05]So, right away, we know that H3PO4 is a source of protons, right? It's a provides us H+. Now, we have to see where are we going to protonate our molecule. We can right away we see H+, we know this is an acid-base reaction.

[00:00:15]So, we have two sites that we could possibly protonate it. We could oxygen can use its electrons to go and grab the hydrogen or our nucleophilic pi bond.

[00:00:21]Now, in deciding which one's going to go and grab it, if our oxygen decides to go and grab this proton, we're going to end up with a positive oxygen and we can't really do anything with that. There's nothing that can happen after. So, it's not going to be productive. But, when our nucleophilic pi bond goes and grabs it, we're going to be left with a positive carbocation and then we can use the electrons from our oxygen to go and attack it. So, that's exactly how our mechanism is going to look. So, first off, we know that our nucleophilic pi bond is going to go and grab H3 and because hydrogen can only have one bond, we're going to break the bond. So, the electrons are going to jump on there and we're going to have the following intermediate. So, we attached our hydrogen on here and now we're left with a positive carbocation. This is going to follow the Markovnikov rule. We're going to put the positive carbocation on the most substituted carbon cuz it's the most stabilized. Now, oxygen can finally jump in and use its electrons to stabilize this positive charge by going and forming a bond there. And it looks like here we're going to form some sort of ring. To figure out the size of our ring, we're going to label the atoms within the ring. So, we have oxygen as one, this carbon we'll label two, this is three, this is four, and this is five. So, we form a five-member ring.

[00:01:18]Our five-member ring is going to look like this. Show another arrow there. 1 2 3 4 5. Then, we know on our carbon two is bonded to oxygen on one and three. 1 2 cuz we form a five-member ring, but don't forget our hydrogen on positively charged. Now, we have to deal with this positive charge. How do we deal with it?

[00:01:34]Well, remember over here, we deprotonated it and we got its conjugate base. So, its conjugate base is equal to beep beep PO4H-?

[00:01:43]So, it's going to go, it's going to grab the proton. Remember, hydrogen can only have one bond. So, it's going to jump back on there and it's going to give us the major product that looks like this.

[00:01:52]But, because this was in an acid environment, we regenerated our acid, right? And so, this is actually an equilibrium with this over here. So these two are in equilibrium. And so that would be the mechanism to determine what the major product would be when we react to this alkene with H3PO4.