Predict the reagents or reactant(s) necessary to complete the ...

Question

Predict the reagents or reactant(s) necessary to complete the following syntheses.

(c) Chemical structure showing alkyne hydration with reactants on the left and product on the right, indicating a synthesis reaction.

Accepted Answer

Hi, everybody. Welcome back. Take a look at our next problem. It says, identify the reagent required to complete the synthesis shown below. And we have a reaction of a single molecule. This molecule is two cyclohexane rings joined together, sharing two carbons in the middle. And it's a symmetrical molecule, each of them having a two carbon substituent that has a triple bond at its terminal end. So between the last two carbons on it and that chain is two carbons away from that shared middle center. And then we have our reaction arrow with a blank box where we're supposed to figure out what reagent should be there. And our product, we have the same cyclohexane rings, but instead of a two carbon chain ending in a triple bond, they now have a two carbon chain ending in an aldehyde. Then we have four answer choices for possible reagents. Choice A has hydrophilic acid and water. So H two. So four and water choice B has two steps. Number one, Mercuric acetate. So HG and then in parentheses, O ac subscript two and water and number two is NABH four and NAOH choice C also has two steps number 103 or ozone. And number 2 h2o 2 or hydrogen peroxide and choice the also two steps. Number one VH three slash thf number two has hydrogen peroxide hydroxide ion and water. So let's think about what's going on in our reaction. We haven't lost or gained any carbons. We still have a two carbon chain, but we started with a triple bond at the end there. So AC C triple bond and that car converted to a CC single bond with a carbon group at the end. So the triple bond has turned into ac C single bond and an aldehyde. So what reactions do we know that convert from a triple bond and then end up with a carbonel group? Well, this reaction would happen, you start with an alky as we do and then have a hydration reaction in this case, that will take you down from an alky to an alkene. But the keen will have an alcohol group added on to it. So that would be an Enna ac C double bond with an alcohol group. And the eal very rapidly undergoes that process of tauter organization to become a key Toone or an aldehyde. So, going down to a single bond between the carbons and then having a carbonel group, ac o double bond on one of the carbons. However, we have three different ways of making this happen. However, we need to think about the fact that that alcohol group to make the anal can add on to either of the carbons in that triple bond. So it may act on carbon one out from the chain or carbon two. So which do we need it to add to, to give us the desired product? Well, we have an aldehyde. So we need it to add to the terminal carbon, which is the least substituted carbon. So that means that we needed to add in an anti Markov Niko edition. And we can recall that our different hydration of all kinds, two of them add in a Markov Neko fashion and only one in the anti Markov Niko. So we need that particular reagent that makes that happen. And that comes about with the process of hydro boring. So we want to look for the reagent that has boron and that would be choice Drbh three slash thf there's our boron and me reagent there. So that re that two step process will carry out the process of hydro oration and oxidation. And that's because when it adds on to the double bond, it goes through a four membered concerted intermediate transition state. So it adds on the alcohol and the hydrogen in a sin fashion. And the oh adds on where there'll be less stich interference. So the least substituted carbon. So we know our correct answer. We need that boron in our reagent. But let's just look quickly at our other answer. Choices to understand why they're incorrect. Choice a with a hydros su acid, this will lead to a ketone. So it will break the triple bond and go to a ketone rather than an aldehyde. So it will add on to that first carbon in the chain. So this adds on in a Markov Niko. I'm just gonna put Mark actually rather than writing out the whole thing again. So that's a Markov Neko edition and that's why it's incorrect. So right kind of reaction, wrong Carmen for it to happen to and joy be same thing. This is our um oxy mercury reduction process and to a was the acid catalyzed. Put that there. We saw that acid there and Choice B we see the mercury on our reagent. So this is the mercury reduction process and it also adds on that carbonel in a Markov Niko fashion. So that's why choice B is incorrect, wrong carbon. And then finally, Choice C we have this ozone in the reagent. And as a result of that, we will end up with a carbon bond on the carbons in our triple bond. But it will add that to both carbons and break all three CC bonds. It's called Ozono sis. And you could see by that lysis ending there, it breaks all three CC bonds. So we don't want that obviously because we want that remaining CC single bond in our molecule. So that's why choice C would not be our reagent of choice. So again, the reagent we need here to complete the synthesis shown below is choice D with the BH three thf as number one. And then number two are H2O 2 ho minus H2O. See you in the next video.

Predict the reagents or reactant(s) necessary to complete the following syntheses.
(c)

Key Concepts

Alkyne Hydration

Reagents for Hydration

Tautomerization

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