Predict the product of the following aldehyde and ketone addit...

Question

Predict the product of the following aldehyde and ketone addition reactions.

(a) Chemical reaction diagram showing an aldehyde reacting with lithium in THF, followed by quenching with H3O+.

Accepted Answer

All right. Hi, everyone. So for this question, let's go ahead and give the product of the reaction below. So let's go ahead and get started. It's worth mentioning here that in the starting material provided we have an aldehyde. And in the first step of this reaction sequence or aldehyde here reacts with an organo lithium compound. Now recall that organo lithium compounds and other organo meal reagents are unique in that they make carbon a nucleo because in the case of this organo lithium compound, carbon is more electron than lithium, meaning it is going to have a partial negative charge and therefore can behave as a nuclear file. So if the carbon of the organo lithium is the nucleo, our electro here is going to be the carbon of the carbo right in our all the height. So after the nucleo attacks the carbonyl carbon, then the car bal becomes an Aloxi ion. The oxide ion is then proton in the second step after acid is added into the solution. So we can use that information to go ahead and draw our final product. Now, I'm first going to go ahead and start off by drawing the six member ring and the isopropyl substituent on the left side because that is not going to change. However, on the right side, instead of drawing out a car bottle, once again, I would instead add a hydroxy or oh group and then I would go ahead and add the R group of the organo lithium reagent. So now I've added the iso beal group that was present in the organo lithium compound. But before we can say that this is going to be our final answer. I want to point something out, right, the car bono carbon of our starting material has been converted from SP two, two P three. And additionally, not only is this carbon, now sp three hybridized, it is also a stereo center. So because of this stereo isomers are going to form because the organo lithium compound, specifically, the nucleic carbon could have attacked the car bono carbon from either side of it. But the problem here is that we have to find a way to show stereo chemistry even if there's already a wedge bond present because now we have to consider this chiral center on the cyclohexane ring. However, if we focus our attention on our new group here, this entire group is actually in front of the cyclohexane rink. And in addition to this, there's also an implied hydrogen from the starting aldehyde that hydrogen in this case is going to be on a wedge facing forwards right away from the cyclohexane rink. So now let's talk about how to show R or S configuration. The first thing we have to do is assign priority to all of the substituents connecting to the Cairo Center. Now, normally priority is decided by the atomic number of the atom directly connecting to the Cairo center. So in this case, we have two carbons connecting to our Cairo center, one oxygen from the hydroxy group and one hydrogen. So oxygen is going to have highest priority since it has the largest atomic number, whereas hydrogen has the lowest priority. So that's number four. So now it's a question of breaking the tie between the carbon of the cyclohexane ring and the carbon of the Isobel substituent. So in a situation like this where priority cannot be determined by the atomic number, you have to consider what else is connecting to each carbon and compare as soon as you find a point of difference, you can then assign priority according to that point of difference. No, the carbon of the cyclohexane ring is connecting to two other carbons and a hydrogen. Whereas the carbon of the Iso beetle group is only connecting to one other carbon and two hydrogens. So that is our point of difference. Carbon has a higher atomic number than hydrogen. So the carbon atom of the Cyclohexane ring is second highest priority and the Isobel carbon is third highest priority. So for ease of visualization, I'm going to go ahead and substitute the Cyclohexane ring and abbreviated as the letter G. So, relative to the chiral center that we're examining, oops wrong color, relative to the Cairo center that we are examining. Recall that the Cyclohexane ring is actually behind us though, I'm going to draw or group G here on a dash, whereas hydrogen is in front, but before we can decide whether or not the configuration is R or S, we have to ensure that the lowest priority is behind us on a dash line. So in other words, we're going to go ahead and swap H with G in this case, right? So after the swap slight correction because I missed a carbon on the iso beetle group. There we go. So in this case, I'm going to go ahead and redraw this molecule so that hydrogen is on a dash. And G here, the Cyclohexane ring is on a wedge. So at this point, now that my lowest priority is behind us, I would trace a path from the highest priority to the lowest priority. And when I do so I can see that I'm going in a clockwise circle. Now, normally this would tell us that the, the configuration is R but because of the swap that we had to make this is actually S configuration. So if this is how we draw the S in an tir, how do we draw the R in an tir? Well, at this point, we cannot change the configuration of the G because at that point, our orientation would completely change, but we can instead change the configurations of positions one and three. So we can place the iso beetle group, for example, on the bottom and the hydroxy group towards the top, this would then result in our configuration. So now we're going to go ahead and translate this into our final answer, right? So I'm going to go ahead and replace G with our psycho hexane ring, right? So for the first in an tir, I would draw the a troop on the bottom and the iso beetle group towards the right side. Whereas in the other, in an to me, I would swap out the order, right, the hydroxy group would go towards the right side and the iso beetle group would be on the bottom and there you have it. So let me just go ahead and open up some space or these stereo isomers. But here are our final answers showcasing the appropriate stereo chemistry. Now its worth mentioning also that for the final answer, I went ahead and I removed the implied hydrogen. So I did not show it in our structure though it is still there, right? So if you stuck around until the end of this video, I thank you so very much for watching and I hope you found this helpful

Predict the product of the following aldehyde and ketone addition reactions.
(a)

Key Concepts

Aldol Condensation

Nucleophilic Addition

Reaction Mechanism

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