For each of the following carbonyl addition reactions, would y...

Question

For each of the following carbonyl addition reactions, would you expect a racemic mixture or a mixture enriched in one stereoisomer? In each case, draw both possible stereoisomeric products.

(a) Chemical reaction diagram showing carbonyl compound reacting with MgBr and H2O, producing an alcohol with stereoisomers.

Accepted Answer

All right. Hi, everyone. So this question is asking us is the reaction shown below expected to produce a mixture enriched in one stereo isomer or a rhythmic mixture. What are the stereo isomeric products in each case? So before we talk a little bit about what it means for a mixture to be enriched in one stereo isomer. I want to just go ahead and discuss this particular reaction and the stereo chemistry of its product or products. Now, our starting material contains a ketone since we have a car panel inside of our four member ring here. So our ketone is reacting with an organo lithium compound followed by an acid quench to produce an alcohol in our final product. Now, organo lithium compounds are examples of organo metallic compounds that we often use to create new carbon carbon bonds. Now, the reason why organo metallic compounds are unique is because they make the carbon atom connecting to our metal, the nucleo because carbon is going to be more electro negative than lithium. So carbon is going to exist with a partial negative charge that makes it nucleic. Now because the organo lithiums carbon atom is nucleic. It's going to attack the electro pilic carbon carbon in our starting material, which is what explains the addition of our ethel substituent in our final product. Now, it's worth mentioning also that the car bono carbon, which is the electro file in this case, is sp two hybridized which means it is plainer or in other words, it's flat. Now, the reason why thats important to us is because the carbon carbon is plainer. The organo lithium compound can attack it from either side, whether that's above or below. This means that the EO group can install itself either in front to form a wedge or from behind to form a dash. So here we end up with different stereo isomers as a result, one in which the EO group is behind the ring itself and the other where the EO group is in front of the ring instead. Now another note about the mechanism here is that the attack of the organo lithium's carbon on the car bono carbon pushes the pi electrons in the car bono upwards towards oxygen giving it a negative charge. That then means it's going to be detonated, excuse me, proton in our next step, which is the addition of acid. So that's why we get an alcohol in the end. Now, normally, right, when we see a mixture of stereo isomers being produced here, we expect to see a reca mixture. This means that generally speaking, there's an equal probability of both stereo isomers existing in solution. But sometimes one stereo isomer may be favored compared to another for a variety of different reasons. This would mean that the mixture is enriched in one stereo isomer. It's enriched in the more favorable cereal isomer. Now, a very common reason as to why one stereo isomer can be favored over another has to do with ster hindrance. But before I go ahead and talk about that, I just realized that in the second isomer, I almost forgot to put the torpedo group. So that's important. There we go. Now, in the stereo isomer on the left side, the hydroxy group and the torpedo group are on opposite sides of the cyclone butane ring. On the other hand, the stereo isomer on the right side has the Turk beetle group and the hydroxy group on the same side of the cyclone butane Rick. Now, if the hydroxy group ends up on the same side of the ring as the torpedo group, this implies that the ethel group which was our nucleo attacked from the front of the car bono itself. On the other hand, if the hydroxy group is on opposite sides relative to the torpedo group, then the ethel group, which was again, our nucleo must have attacked from the same side as the torpedo group. Now, the third beo group is remarkably bulky and it's large in size, right? So as the nucleic ethel group attempts to approach the electro file, which was the carbon carbon, that approach is made more difficult by the hysteric hindrance caused by the presence of the T beetle group. Now, on the other hand, if the ethel group attacks the carbon carbon from the front side, it's not going to encounter the turtle group, meaning it experiences less STAIC hindrance. And therefore, that approach is more favored. So with that, we've arrived at our final answer because not only have we drawn the two different stereo isomers expected, a mixture enriched in one stereo isomer is expected. And the reason it is ex expected is because the formation of one would require the nucleo to experience more asteric hindrance compared to the other. So there you have it, here is our final answer. And so with that being said, thank you so very much for watching. And I hope you found this helpful.

For each of the following carbonyl addition reactions, would you expect a racemic mixture or a mixture enriched in one stereoisomer? In each case, draw both possible stereoisomeric products.
(a)

Key Concepts

Carbonyl Chemistry

Stereochemistry

Nucleophilic Addition Mechanism

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