You have been called in as a consultant for the firm...

You have been called in as a consultant for the firm Alcohols Unlimited, which wants to build a plant to produce 3 -methyl-I-butanol, $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{OH}$. The research director, Al Keyhall, has proposed that acid-catalyzed hydration of 3 -methyl-1-butene be used to prepare this compound. The company president, O. H. Gruppa, has asked you to evaluate this suggestion. Millions of dollars are on the line. What is your answer? Can 3 -methyl-1-butanol be prepared in this way? Explain your answer.

Key Concepts

Markovnikov's Rule

Markovnikov's rule states that in electrophilic additions to unsymmetrical alkenes, the proton adds to the carbon bearing more hydrogen atoms, while the nucleophile adds to the more substituted carbon. This is due to the fact that the intermediate carbocation formed on the more substituted carbon is more stable, and as a result, the final product reflects this regiochemical preference.

Acid-Catalyzed Hydration Mechanism

Acid-catalyzed hydration involves the addition of water to an alkene in the presence of an acid catalyst. The mechanism proceeds via the protonation of the alkene to form a carbocation intermediate, followed by nucleophilic attack by water and subsequent deprotonation. This mechanism inherently follows the pathway dictated by carbocation stability.

Carbocation Stability

Carbocation stability is a central concept in many reaction mechanisms, particularly in electrophilic addition reactions. More substituted carbocations are stabilized by hyperconjugation and inductive effects, which leads to regioselective outcomes in the reaction. The preference for forming a more stable carbocation influences which product is predominantly formed.

Regiochemistry in Electrophilic Additions

Regiochemistry in electrophilic addition reactions is determined by the electronic and steric factors that govern the formation and stability of reaction intermediates. In acid-catalyzed hydration, the regioselectivity—specifically, the site at which the hydroxyl group attaches—is closely tied to the stability of the intermediate carbocation, which follows Markovnikov's rule.

Transcript

00:06 This question asks us how we can make each of these alcohols starting with three methyl one butyne.

00:12 So for a part one, we are making two methyl two butanol.

00:18 And so the first thing that we're going to have to do here is reduce this alkyl to an alkyne.

00:27 So we have to do that before we can do anything else because otherwise we'll be left with a pie bond in our final product, which we don't want.

00:35 So we'll start with this alkyne and we'll do h2 and the lindlar catalyst.

00:46 And that will give us an alken that will look like that.

00:53 And then another thing to notice about this one is that there has been a shift here.

00:59 So on this, our methyl group is on carbon three, but on our final product it's on carbon two, which means that there was some sort of shift.

01:09 And that's going to be a proton shift and it's going to happen while we're putting on that oh -h.

01:13 So to put on that oh -h, we want it on the internal carbon.

01:17 So we're going to use acid -catalyzed hydration.

01:21 So it'll be h -plus, probably an h -2 -s4 or a similar acid with water.

01:26 And the intermediate of that reaction is going to look like this.

01:29 So the pyebon is going to come and grab the h.

01:32 And we're going to get a carbocation right here, which is a secondary carbocation.

01:39 But that can be made more stable if we do a methyl shift here, make it a tertiary carbocation.

01:47 So we'll end up with, oops, let me draw that better.

01:53 We'll end up with this carbocation instead if we do that methyl shift.

01:58 And that will give us the methyl group in the right place right here.

02:01 And then we can add, have the water go ahead and attack that carbocation, and we will be left with our product.

02:12 The next alcohol that it wants us to make is three methyl one butanol.

02:16 So again, starting with that three methyl one butyne...

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