Propose a mechanism for the following reaction that explains w...

Question

Propose a mechanism for the following reaction that explains why the configuration of the asymmetric center in the reactant is retained in the product:

Chemical reaction mechanism illustrating retention of configuration at an asymmetric center during an SN2 reaction.

Accepted Answer

Hey, everyone. And welcome back for the reaction. Given below, provide a suitable mechanism that illustrates why the retention of the reactants configuration at the chiro center is observed in the product. Now, the given reaction is between a slightly complicated structure that has two carboxylate and ions as well as an amino group. And the structure undergoes a reaction in the presence of sodium nitrite hydrochloric acid to produce a cyclic structure, which is a cyclic because we have our coo R group as well as one of the remaining groups. Essentially what we're going to do here. We're going to remember one important thing. Whenever we're using sodium nitrite in the presence of hydrochloric acid, We are able to turn our Amino group NH two into nitrogen. And specifically, that would be another nitrogen via a triple bond. And of course, the one that has four bonds is positively charged, we have a formal positive charge. So this is our first step. We are going to start by drawing our starting material. Let's add our carbon atoms in the chain, we have 1234 carbon atoms. So 1234 and then we are going to add our carboxylate, then our amino group pointing up hydrogen pointing down. So now according to our mechanism, here, we are adding sodium nitrite in the presence of hydrochloric acid. This is our first step. And as we already said, we are going to turn our amino group into Diro. So we got our intermediate. Now, the reason why we did it, why we did it is just because currently we have a very good living group. You may think about this as removal of nitrogen gas. If we can form an two, that's a very favorable reaction. However, we need a nu file for this reaction. And actually we have an adjacent nu which is carboxylate. Now we are going to expand carboxylate into its complete form. So that be carbon bonded to oxygen in a carbonyl group. And then another oxygen negatively charged by let see the carbon atom within the carbo group. Now there are two carboxylate and ions actually in the structure. But of course, the closest one will react first, right, the rate of the reaction for this one will be faster. And therefore, we can illustrate an essence, a reaction that happens at first the negatively charged oxygen, it attacks the electro Pyle carbon that has the nitrogen bondt set. And then we have a simultaneous loss of the leaving group which is nitrogen gas. So we can control the resultant intermediate. And in that intermediate, we will have a ring formed specifically what do we get into here is just a sign our inversion of configuration to begin with. So basically, if hygiene was pointing down now, it will be pointing up because we should remember that essence reactions undergo an inversion of configuration. So hydrogen is pointing up on a wedge now because we're forming oxygen, carbon bond, We have a three membered ring where two carbon atoms are bonded to oxygen and oxygen will be pointing down, right, because there's an inversion of configuration and one of the carbon atoms is still bonded or based like double bond, that's the oxygen. So now that we got our intermediate, we have to think how can we actually get that ring? And simply, you may notice that we still have one of the carboxylate anions remaining due to the presence of that carboxylate that we are going to expand. And of course, we can also add nitrogen gas formed in the previous stop. We may now think about an essence of reaction in which we are going to expand our carboxylate first. So we are going to clearly show how we have coo negative and the negative charge on oxygen will attack the electrophysics position within our three member dr. Now, in this case, we are going to attack carbon that is bonded to one oxygen only instead of carbon that is bonded to two oxygens. That's basically because the two adjacent oxygens what vitro electrons to each of them. And basically make that carbon less electrolytic than the one that has one oxygen bond to directly. So the carboxylate and I will attack the oxygen atom within the three member. My apologies, it will attack the electro filic position are basically the carbon atom that is bonded to one oxygen only. And then if we are creating that bond, then we have to break the bond between carbon and oxygen. Now because this is in essence a reaction since we are attacking the electro Pyle carbon followed by the loss of the lead group simultaneously. Another essence or reaction will show us an inversion of configuration. We are forming a ring at this step and to draw it properly, we can just enumerate our carbon atoms. So let's enumerate them 1234, Then we have five. So we understand that we will have a six member, drink oxygen will be the 6th atom in it. Meaning we can simply draw our sex member ring with our carbon group. Now, if we start with oxygen and then go counter clock, we have 12, 345 And then we're going to bond carbon five to oxygen just as we showed it in the mechanism. And because there's an aversion of configuration of position five, we're going to turn hygiene that was pointing up into a dash so that it's pointing down now, meaning the carboxylate and iron formed coo negative must now must be now pointing up because it was originally pointing down. So let's add that as well coo negative. And we got our product. Now thinking about the mechanism which we can label in green as our final answer, we can just conclude why there's no net inversion of configuration. That's basically because we have two successive SN two reactions in the first reaction, there's no essence reaction. We're just converting an amino group into nitrogen. But then an intra molecular SN two reaction takes place. So we have an inversion of configuration for the first time after that, when the three member dr is formed, we have another essence reaction for the second time. So that's why overall we don't see any, we, we see inversion. We see a retention of configuration actually because one essential reaction sort of cancels out the other one whenever we are referring to configuration only. That's the main reason based on our answer, we may conclude that the correct answer to this multiple choice question is c thank you for watching.

Propose a mechanism for the following reaction that explains why the configuration of the asymmetric center in the reactant is retained in the product:

Key Concepts

SN2 Reaction Mechanism

Asymmetric Centers

Diazotization Reaction

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