Point out the flaws in the following incorrect Grignard synthe...

Question

Point out the flaws in the following incorrect Grignard syntheses.

(a)

Accepted Answer

Hey everyone and welcome back in today's video, we are going to solve the following problem. Can you identify what is wrong with the following granular synthesis? When we look at a given reaction, we essentially notice that the starting material has a bromo substitution step number one is the addition of magnesium in either. So that's how we may produce our granite region. Then we're adding a carbon compound which has an allied group and finally we have an acidic work up which produces a dial. So let's see how this reaction is supposed to work based on the final product. We are starting with our initial substance. And the problem suggests that in the first step we're adding magnesium in the presence of ether. Now keep in mind that the substance we're going to outline here are not necessarily correct. We are just trying to predict whether or not this product is possible and how it was formed. Right? How could we form that product based on these three reactions. Now, the problem assumes that we are firstly forming a great nerd region, right? Because we're using magnesium in the presence of ether and we have an al killed bromide. Now, magnesium is incorporated into the chain and we are obtaining our grain yard rage and that would be M G B R. So we have formed our green operation And then the next step we're adding a carbon compounds. We're going to draw that Aldo hide there's hydrogen on one end and on the other end we have a psycho psycho proposal group, recall that the greener region essentially attacks the carbonell and then we are breaking the pi bond to form our elk oxide and iron. Now, if you think about the formation of the product, we may simply redraw the original substrate with no pi bonds. So that be our elk, oxygen and iron. First on the left, we have our hydrogen on the right, we have our cycle appropriate group. And now, essentially what we're doing, we're adding two carbon atoms to begin with. And then at position number two, we have an O age group. Finally, we're protein eating it. So we can say that in the third step when we perform that acidic high troll is us. The proton gets abstracted by Alcock side and we get our final product, we may not worry about this implicit hydrogen. And let's just see if this is exactly what we expect to get. So we get our cyclo proposal bond, it's a carbon atom that would now have no age group. Right? So this is one carbon, then we have 12 more. So let's draw them out. 12 and that second one has in a wage group. And this is exactly the product that we're seeing. But let's think about it. This this everything makes sense here. So let's start a step by step analysis. And if we look at the first step, yes, we're forming the green region by incorporating magnesium here. But aren't these conditions acidic notice that there's an acidic proton here specifically oxygen, hydrogen bonded oxygen implies that sexy hygiene would be partially positive because there's a polarization towards oxygen, which is more electro negative. So this hydrogen is acidic. Now, what's actually happening is that because this ha jin is acidic and magnesium is a metal which can display such a ha jin magnesium as a group to a metal. Right? So it can perform a single replacement reaction. Recall that from general chemistry. Now, if we perform a single replacement reaction or single displacement, if you wish, we may essentially understand that we're producing hydrogen gas. So in the first step, because magnesium is more reactive in that single replacement reaction than than is forming the actual green reagent due to that reactivity, it's more preferred for magnesium to displace that hydrogen. And what's happening is that when hydrogen is this place we're producing hydrogen gas plus Elk oxide and iron. And then we have two units of these, Right, Because magnesium would have a positive to charge in that single replacement reaction. So these are actually our products. And now you may see that there's no more proton. Right. And magnesium has been used up. Now, what's happening is actually if you think about the Elk oxide, it might for many box side if we go even further because there's a good leaving group. So we may also form an epoxy over here. That's not really so important just sufficient to understand that The reason why there's a problem with the synthesis is in the first step step one. And we can conclude that any green yard region cannot be formed in an acidic medium. That's basically because that acidic hydrogen would be displaced by magnesium. Right, just as we have shown, and this is why the reaction doesn't proceed further the way we expect it to proceed. Now going forward, we may also understand that if we really want to make this reaction work, we first of all have to protect the alcohol group and then perform all of the steps outlined in the synthesis and that's our final step. We would just be protected and we would restore the alcohol group. However, regarding this problem, the correct answer choice would be be the problem with this synthesis is the first step of the reaction. A greener region can never be prepared in a reaction medium with a proton source. That will be it. Thank you for watching

Point out the flaws in the following incorrect Grignard syntheses.
(a)

Key Concepts

Grignard Reagents

Nucleophilic Addition

Functional Group Compatibility

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