 So, again we're going to prepare an acid chloride from a carboxylic acid using thionyl chloride. Again, remember, I guess we'll over here, we'll draw the resonance forms of thionyl chloride. So that's thionyl chloride, but it would prefer, this is the major resonance form, it's going on the right here, because of that overlap, that, those pi, those fields. So anyways, notice the only difference we're doing is taking this hydroxyl group and changing it to a chlorine. I'm going to erase this one. So I'm just going to draw it looking like kind of a carbonyl type, because you guys are very familiar with that. Well remember, positive charge there, so electrons are very attractive to it. So what's going to happen is these electrons here are going to want to see, they're going to see that and want to attack it, but they need to be instigated to attack it from some other way. So these electrons here are going to come down and make that bond there. And then that bond is going to attack there, and it's going to push those up if you want to. So it's again the same mechanism as we showed before, except all in one step. Just like when you attack a carbonyl, that double bond is going to come and snap back shut and kick out your best leaving group. In the case of the leaving groups that we have associated around that sulfur atom, the best leaving group is going to be the chlorine atom. It might be this thing that you just attacked, but that's just going to go back that way. So it's not going to produce productive reaction. So the best leaving group to make the reaction go forward is that chlorine. That happens the reaction goes. Now you've got this intermediate. So notice this portion looks a lot like thionyl chloride. What's going to happen now? Deep protonation step. It doesn't necessarily, in fact, let's not say that it's with that chlorine. Well, we could say it's from that chlorine, because we've got more than one thionyl chloride in here. We'll just say it's from that chlorine because what other bases are there for you guys? Well, we've made HCl. Again, like I said, you've got more thionyl chloride in there, but HCl itself is not that well stuck together. So either way, you're going to have the Cl or ACL in your mixture chloride anion. It's going to come and attack that electrophilic carbon there, causing those electrons to migrate up to that oxygen just like you know that. This thing here is a super good leaving group. Why? Because you've got this sulfur. I mean, sulfur big, you're going to make sulfur dioxide. But you've got all of these resonance structures that this conjugate base could have. So that's going to be a very good leaving group. And in fact, it's going to be a better leaving group than the chloride. That's why the chloride doesn't get kicked back up. The other reason it's a good leaving group, like I said, is you're going to make sulfur dioxide, which is a very stable molecule. Just like when we make carbon dioxide, it'll make water or hydrogen sulfide or anything like that. So I'm just going to keep this in the same confirmation that I don't have to do any rotational change. This is what I was talking about before, is now you've got a choice which is the better leaving group. The chlorine, because this is going to come back down, snap back down and it's going to have to decide which leaving group goes. Well, the chlorine we know is a good leaving group. But if we kick this guy off, it makes a stable molecule there, SO2, and that'll kick that chlorine out. And that chlorine can go back and be the base for the next one. So that's why I kind of wanted to say there is a base in there, but we've got to have it produced first. And remember also HCl was made in this step. Again, those aren't super attracted to each other, so it could have been that one. I'm going to erase the top so I can finish this mechanism. So once that happens, we've made our acid chlorine. And again, I'm going to keep it in that same confirmation. We can turn it over in a second. This got kicked out, so we still have the chlorine there. So everybody sees that's the product we were going for. We made also SO2 like that. Everybody cool with that one? And we also made the Cl minus. So that's the Cl minus that was going to be in the next step. It's going to deprotonate. So I guess this is the organic product that we were concerned about. This is the stable molecule that drives the reaction and makes this portion here. Any other questions?