Acids, in a reaction called the pinacol rearrangement. (a)...

Name: Problem 77, Chapter 9: Organic Chemistry
Uploaded: 2026-03-08T16:11:30-08:00
Duration: 5 min 29 s
Channel: Susan Hallstrom
Description: acids, in a reaction called the pinacol rearrangement. (a) Draw a stepwise mechanism for this reaction. (Hint: The reaction proceeds by way of carbocation intermediates.) (b) Assuming that the pinacol rearrangement occurs via the more stable carbocation, draw the rearrangement product formed from diol D.

acids, in a reaction called the pinacol rearrangement. (a) Draw a stepwise mechanism for this reaction. (Hint: The reaction proceeds by way of carbocation intermediates.) (b) Assuming that the pinacol rearrangement occurs via the more stable carbocation, draw the rearrangement product formed from diol D.

Key Concepts

Migratory Shifts in Rearrangement Reactions

Migratory shifts, such as hydride or alkyl shifts, are key steps in rearrangement reactions. In these processes, a group adjacent to a carbocation migrates to the positively charged center, forming a more stable intermediate. Such shifts are crucial in the pinacol rearrangement, as they allow the intermediate to rearrange into a structure that can eventually form a stable carbonyl compound.

Carbocation Stability

Carbocation stability plays a crucial role in determining the outcome of reactions that involve rearrangements. Stability is influenced by factors such as hyperconjugation, resonance, and inductive effects. The more substituted or resonantly stabilized a carbocation is, the more favorable its formation, which often dictates the pathway of subsequent molecular rearrangements.

Acid-Catalyzed Reaction Mechanisms

Acid catalysis in organic reactions involves the use of protons to activate a molecule, often by protonating functional groups like hydroxyls, which makes them better leaving groups. This facilitates the formation of reactive intermediates such as carbocations, enabling subsequent rearrangements or substitutions to occur in a controlled manner.

Carbocation Intermediates

Carbocations are positively charged carbon species that are key intermediates in many organic reactions. Their formation is often the rate-determining step, and they are stabilized by electron-donating groups. In rearrangements, the initial carbocation may undergo structural shifts such as hydride or alkyl shifts to form a more stable carbocation, ultimately guiding the pathway to the final product.

Pinacol Rearrangement

The pinacol rearrangement is a well-known acid-catalyzed reaction in organic chemistry where a diol undergoes a structural reorganization to form a carbonyl compound. This reaction typically starts with the protonation of one of the hydroxyl groups, followed by the loss of water and formation of a carbocation intermediate, which then undergoes a rearrangement process to yield the aldehyde or ketone product.

Transcript

00:01 Let's see, i think it'll go pink.

00:03 In this problem, we're asked to consider the information here.

00:06 One, two dials are converted to carbony compounds when treated with strong acids and something called a pinnacle rearrangement.

00:14 We're asked to do this stepwise mechanism, and then assuming that the rearrangement occurs for a more stable carbocation, rather rearrangements for the product formed d.

00:25 Okay, so here, we're going to start with this, everything that i've written so far is given.

00:31 So i'm going to add these and draw arrow to here and then draw an arrow to here.

00:43 And that will give me what i've got.

00:48 And this will give me the following.

01:05 So now this is the whole different part.

01:10 This will give me.

01:35 Okay.

01:36 And then we're going to add this with this will give me.

01:43 This is going to move here.

02:10 There we go.

02:10 And then i better switch colors.

02:13 I didn't need to do it.