Two products are observed in the following reaction.

Question

a. Suggest a mechanism to explain how these two products are formed.

b. Your mechanism for part (a) should be different from the usual mechanism of the reaction of SOCl₂ with alcohols. Explain why the reaction follows a different mechanism in this case.

Accepted Answer

Hey everyone. Let's do this problem. It says two products are obtained from the reaction given below. Propose a suitable mechanism to show why two products are obtained through this reaction. This mechanism should be different from the usual mechanism of the reaction of vinyl chloride with alcohol. So these vinyl chloride is often the best re agent for converting an alcohol to an alcohol chloride, which is what we see here. And the mechanism for this resembles an S. N. One reaction except the nuclear file is delivered to the carbo catan by the leaving group, usually giving the retention of configuration. And in sN one we could have a mixture of retention and inversion of configuration. So since the problem says that this specific mechanism is different than the general mechanism for a reaction of alcohol and vinyl chloride. Let's first look at the usual mechanism and we will use that as sort of our structure or general guide for our mechanism. But we'll notice where there will be differences. So in the usual mechanism we have our alcohol which has two lone pairs on the oxygen in our final chloride. If you don't already, you might want to pause now and get a snack because this is gonna be a long video. So these vinyl chloride is attacked by this oxygen, the hydroxy oxygen onto that electro Felix sulfur. And those electrons will swing up onto the oxygen. So now we have the oxygen attached. Oops, that's a single bond now on the oxygen still have a lone pair on our sulfur In three lone pairs on are now negative oxygen. And those electrons will come right back down to form that double bond which will kick off the chlorine. Okay, so that chloride ion is created expelled but it's going to come back and get its revenge. And what I mean by that is that chloride ion now Is going to D protein eight. This hydrogen, I forgot my positive charge on oxygen. So that chloride ion which is negative will come take this hydrogen which will form a chlor oh sulfate ester. So let's draw what that looks like. And we know this isn't Esther because it has that formula R. O. R. And now we also have Hc L. Okay so again this is a chlor oh sulfate Esther. So now in the next step this claure sulfate ester is going to ionized if that our group is secondary or tertiary. So that means it will sort of separate itself and it will become a cat ion while the rest of the structure is are an ion. Okay, so now we've created an ion pair. So now the sulfur atom is quickly going to deliver that chloride to the carbo cat island. Okay, so that our group that just popped off, it broke up with the oxygen and that chlorine is going in for the steel. Okay, it's going to attack it right there as the oxygen swings down its electrons to sulfur. Okay and this step is fast, It happens quickly and when the R. Is primary, that chloride ion is probably bonding to the carbon at the same time as this sulfur or sorry, the R. O. Bon is breaking, so this one is breaking at the same time that this one is being made if the R group is primary. Okay. So then we're left with R. C. L. R alcohol, a light has formed and this is what will remain of the final chloride. Okay. So let's sort of try to apply this to our given reaction and see where things differ. Okay, so our alcohol looks like this, a five member ring with deuterium and chlorine on the same or sorry, that's our product deuterium and alcohol group on the same carbon we have a double bond. So in the first step this alcohol is attacking our vinyl chloride. So let's draw our tiny local ride. The oxygen attacks the sulfur. So now that oxygen is attached to the sulfur and has a positive charge and this other oxygen has a negative charge. And just in this step two, they will swing down those oxygen electrons to kick off the chloride ion. Right, so we're following the same steps so far and now that chlorine that just popped off the chloride ion D protein 8s, that former alcohol group. Okay, so far so good. Same mechanism. So we have just lost H. C. O. Right and we're left with deuterium still these oxygen, so this is our ester. Right? R. O. R. Oops. Okay, so after our Esther what happens? We have an ion pair? Right, so that our group is going to leave. We can draw the electrons from the bond going on too, the other side of the oxygen. And that chlorine ion is also going to leave. So we will have our chlorine ion, S. 02. And now our ion. So what is our ion going to look like? I forgot, my double bone and all of these. So we'll have our deuterium and there's going to be a positive charge right here on that tertiary carbo cat. I'll but that charge is next to a pi bond. Right? So we can have some resonance here. So that double bond can move over to create another carbo cat, on which has the double bond here in that carbon that has the deuterium and our carbon Canton is now secondary in this structure. So in our last step, when the chlorine goes and attacks our our our plus positive ion, right? It can attack in two different spots now. So we can either have the chlorine atom attacking up here at this tertiary carbo cut on or we can have it attacking down here at our secondary carbo katan. Ah So that's why we have two different products. Right? So attacking the carbo cat ion in those two different positions gives us the following two products that we see up above. So in this one the chlorine adam is alternating carbons from the deuterium or we have it where the chlorine adam is sharing the carbon with the deuterium and replacing right where that alcohol group was in our reactant. And this gives C. To be the correct answer to this problem. Just a couple of quick corrections. Before we finish, I noticed I was missing a lone pair here and this is not a tertiary carbon cat on. They are both secondary. I mistook the deuterium for a carbon group and saw it as tertiary. Okay, so secondary carbo cantons and that lone pair there. That's it for this one. I hope this video is helpful. And thank you for watching.

Key Concepts

Mechanism of SOCl2 with Alcohols

Deuterium Labeling

Alternative Mechanisms in Organic Reactions

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