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Chapter 13: Problem 24

What product would you expect from Claisen rearrangement of but-2-enyl phenyl ether?

Short Answer

Expert verified
The product is 2-but-1-enyl phenol.

Step by step solution

01

Identify the Structure

First, identify the structure of but-2-enyl phenyl ether. It consists of a phenyl group (benzene ring) attached to an ether link, which is bonded to the but-2-enyl group consisting of a four-carbon chain with a double bond at the second position.
02

Understand Claisen Rearrangement

The Claisen rearrangement is a [3,3]-sigmatropic rearrangement involving allyl vinyl ethers or allyl phenyl ethers. In this rearrangement, the ether linkage is broken, and new carbon-carbon bonds form to generate an ortho-substituted phenol.
03

Predict the Transition State

Visualize the transition state where the electrons move in a concerted fashion. The allyl group (but-2-enyl here) will rotate to allow a [3,3] orbital overlap, facilitating the rearrangement.
04

Determine the Product

In the Claisen rearrangement of but-2-enyl phenyl ether, the allyl group (but-2-enyl) shifts to the ortho position of the phenol, resulting in the formation of 2-but-1-enyl phenol.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

But-2-enyl Phenyl Ether
But-2-enyl phenyl ether is an organic compound that plays a crucial role in the Claisen rearrangement. It consists of two main parts:
  • A phenyl group: This is a six-carbon benzene ring, which is aromatic and stable. It's an important structural component in many organic molecules.
  • An ether linkage: In this compound, it connects the phenyl group to the but-2-enyl group, which is critical for the rearrangement process.
The but-2-enyl group is a four-carbon chain with a double bond between the second and third carbons. It's this unsaturation that makes but-2-enyl phenyl ether a suitable candidate for the Claisen rearrangement. The presence of both the phenyl group and but-2-enyl group allows for the molecular interactions necessary to enable reaction dynamics, leading to the rearrangement into a different structure.
Sigmatropic Rearrangement
Sigmatropic rearrangements are fascinating reactions in organic chemistry characterized by the movement of a sigma bond across a pi system. In simpler terms, they involve the migration of atoms or groups of atoms within a molecule, often resulting in a significant change in structure. In a Claisen rearrangement, which is a type of [3,3]-sigmatropic rearrangement, the change involves the movement of a carbon-carbon sigma bond. Here are some key points:
  • The original ether linkage is broken, and instead, new carbon-carbon bonds are formed.
  • These rearrangements are concerted, meaning they occur in one smooth step without intermediates.
  • It involves the overlapping of orbitals in a unique way, known as the [3,3] sigmatropic shift.
  • The result is usually a more stable molecular structure.
This rearrangement allows but-2-enyl phenyl ether to transform, aiding in the creation of new, often biologically important, molecules.
Ortho-Substituted Phenol
The term ortho-substitution refers to a specific location of substitution on the phenol ring following a chemical reaction, such as the Claisen rearrangement. For phenol, the ortho position is adjacent to the hydroxyl group (-OH). This specific placement is crucial because it impacts the chemical properties and possible reactions that the molecule can undergo. When but-2-enyl phenyl ether undergoes a Claisen rearrangement, it transforms into an ortho-substituted phenol:
  • The but-2-enyl group shifts from the ether linkage to the ortho position on the phenol ring.
  • This rearrangement results in 2-but-1-enyl phenol, where the double bond initially part of the allyl group now sits next to the phenolic hydroxyl group.
  • Ortho-substituted phenols are valuable in organic synthesis, offering pathways to creating complex organic molecules.
Thus, understanding the shift to an ortho-substituted phenol is essential to grasping the full implications of the Claisen rearrangement for creating diverse and stable aromatic compounds.

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Most popular questions from this chapter

Show the products obtained from addition of methylmagnesium bromide to the following compounds: (a) Cyclopentanone (b) Hexan-3-one

Epoxides react with Grignard reagents to yield alcohols. Propose a mechanism.

Evidence for carbocation intermediates in the acid-catalyzed dehydration of alcohols comes from the observation that rearrangements sometimes occur. Propose a mechanism to account for the formation of 2,3-dimethylbut-2-ene from 3,3-dimethylbutan-2-ol.

A compound of unknown structure gave the following spectroscopic data: Mass spectrum: \(\quad \mathrm{M}^{+}=88.1\) \(\mathrm{IR}:\) \(3600 \mathrm{~cm}^{-1}\) \(\begin{array}{ll}1 \mathrm{H} \mathrm{NMR}: & 1.4 \delta(2 \mathrm{H}, \text { quartet, } J=7 \mathrm{~Hz}) ; 1.2 \delta(6 \mathrm{H}, \text { singlet }) ; \\\ & 1.0 \delta(1 \mathrm{H}, \text { singlet }) ; 0.9 \delta(3 \mathrm{H}, \text { triplet }, J=7 \mathrm{~Hz}) \\ { }^{13} \mathrm{C} \text { NMR: } & 74,35,27,9 \delta\end{array}\) (a) Assuming that the compound contains \(\mathrm{C}\) and \(\mathrm{H}\) but may or may not contain O, give three possible molecular formulas. (b) How many protons (H) does the compound contain? (c) What functional group(s) does the compound contain? (d) How many carbons does the compound contain? (e) What is the molecular formula of the compound? (f) What is the structure of the compound? (g) Assign the peaks in the \({ }^{1} \mathrm{H}\) NMR spectrum of the molecule to specific protons.

As a rule, axial alcohols oxidize somewhat faster than equatorial alcohols. Which would you expect to oxidize faster, cis-4-tert-butylcyclohexanol or trans-4-tert-butylcyclohexanol? Draw the more stable chair conformation of each molecule.
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