When cis-2,4-dimethylcyclohexanone is dissolved in aq...

Question

When cis-2,4-dimethylcyclohexanone is dissolved in aqueous ethanol containing a trace of NaOH, a mixture of cis and trans isomers results. Propose a mechanism for this isomerization.

Accepted Answer

Hey everyone and welcome back in today's video. We are going to solve this problem which reads a mixture of CIS and trans eyes MERS is obtained by dissolving trans five promo two methods cycle hex alone in an aqueous solution of sodium hydroxide show the mechanism of this is memorization. What we're going to do here. We are going to draw cycle Jackson on first. So that would be our six member ring. Right? And because it's psycho hacks and when we understand that we must have a carbon group bon it'll ring. So we got our cycle hex unknown and now positions two and five. So let's suppose that this is our position number two because the carbon group respondents position number one, that's 2345. So these two positions have substitutions. Now, position two contains a metal group. So let's suppose we added on a watch pointing up and because it's trans position number five would have the bromo substitution pointing down. Right, essentially, the two substitutions must have trans arrangement. Okay, so this is our starting structure. And what we understand is that we're dissolving this compound in an aqueous solution of sodium hydroxide, we're going to identify our stake protons. And because we have a carbon group, the alpha position will contain the most acidic proton here, specifically we have two alpha positions over here and here. And because we are going to form an Enel eight. We are going to consider this proton over here Because that would form a more stable in a late right. Notice how we would form a double bond and the metal group would stabilize the result and Enel. So that's that we're considering this proton only as the most acidic proton which upon elimination would form a more stable Channel eight. So now when we're thinking about our mechanism, the hydroxide and I and from sodium hydroxide, which the associates to release hydroxide essentially attacks that proton. Right? We have that proton capture and we're transferring those carbon hydrogen electrons into the formation of a double bond. And when we're forming that pi bond over here, we're going to break the adjacent pi bon and transfer these bonding pi electrons in the form of a lone pair on oxygen. So we get our insulating this stuff. Let's just draw it now. Roaming is not affected, it's not participating in this reaction. Right. So we are just going to add roaming in its original configuration. Now, what we notice here is that we get a planer sp two hybridized carbon atoms. So we can essentially draw a metal group on a solid line that we can throw our result on five bon and then we have a single bonded oxygen to that carbon with a formal negative charge. Right? Because we have transferred these bonding electrons in the form of a lone pair. So now in a late is plainer and we are going to protein eight. That now the reason why explainers basically because you notice that these two carbon atoms are sp two hybridized. Right. And now we are going to protein eight. That essentially you may recall that we're restoring our pi bonds. So we are going to use these lone pair electrons. And then upon breaking that pi bond which gets protein aided by the water molecule which we have formed in the first step upon breaking the pi bond, there's a three year rotation of that metal group before the proton capture takes place. So we may either add that proton from the top face or the bottom phase. Right. So we will have two possibilities, meaning in one case the metal group will be pointing up and in the other case the metal group will be pointing down. So because we have two possibilities we're going to have to products. So we have that proton capture which is full by the loss of the leaving group hydroxide and that's pretty much it. We can outdraw two structures. The first one is we discussed would contain the original ring. Now nothing changes with respect to bro mean, we can just add it on a dash. As we previously discussed here, we are reforming the carbonell group. And now as we sat, if the proton is added from the top face, we would essentially have the metal group pointing down. Right, so we can draw that metal group pointing down and that would be our cece isenberg. The reason why it says is because bro mean and the metal group they're pointing in the same direction with respect to the ring, they're both pointing down plus our trans eyes more so now to throw the trans is more, we're going to add our six member ring bro mean would be at brimming with retainers original configuration. And now if we are adding hygiene from the bottom phase then the metal group would be pointing up on a watch. Right? And over here we have our carbon group restored. So that would be our trans compound. Because if you notice blooming and metal they're pointing in opposite directions with respect to the plane of the ring. So we got our mechanism we can essentially label as our this whole mechanism is our complete mechanism and the answer to this problem because the problem was asking us to show the mechanism for this isomerization. And if we briefly discuss it, we understood that we saw two alpha positions around our carbon group and we chose to D protein eight. This alpha position because as you notice, it forms a more stable email sees the presence of death metal group. Now the protein nation step can take place two different ways I whether we add hydrogen from the top or the bottom phase because during the cleavage of that pi bond, there's a free rotation of the metal group and therefore it can either be pointing up or down in the final product. So that's how we get cIS and trans products based on this mechanism. We can conclude that the correct answer choice, the small pool choice question is C. However, if you have any questions, don't have States, leave your comment down below in the comment section and thank you for watching.

When cis-2,4-dimethylcyclohexanone is dissolved in aqueous ethanol containing a trace of NaOH, a mixture of cis and trans isomers results. Propose a mechanism for this isomerization.

Key Concepts

Isomerization

Nucleophilic Catalysis

Equilibrium and Reaction Conditions

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