Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook

Mullins 1st Edition

Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring

Problem 37

Chapter 23, Problem 37

Oxidation of the phenol shown gives a single quinone product. Predict this product and explain why it is the only one formed.

Verified step by step guidance

Identify the starting material: The phenol shown in the image is 4-nitrophenol, which has a hydroxyl group (OH) at the para position relative to the nitro group (NO2) on the benzene ring.

Understand the reaction conditions: The reagent used is chromic acid (H2CrO4) in water, which is a strong oxidizing agent commonly used to oxidize phenols to quinones.

Predict the oxidation process: In the oxidation of phenols, the hydroxyl group is converted into a carbonyl group, forming a quinone. The para position of the phenol is typically oxidized to form a para-quinone.

Consider the influence of substituents: The nitro group (NO2) is an electron-withdrawing group, which stabilizes the formation of the quinone by withdrawing electron density from the ring, making the para position more susceptible to oxidation.

Explain the formation of a single product: Due to the electron-withdrawing effect of the nitro group, the para position is the most reactive site for oxidation, leading to the formation of a single para-quinone product, rather than multiple quinone isomers.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Phenol Structure and Reactivity

Phenols are aromatic compounds with a hydroxyl (-OH) group attached to a benzene ring. Their structure allows for resonance stabilization, which enhances their reactivity in oxidation reactions. Understanding the specific phenol structure is crucial for predicting the oxidation products, as the position of the hydroxyl group influences the outcome.

Oxidation Mechanism

Oxidation in organic chemistry typically involves the loss of electrons or an increase in oxidation state. In the case of phenols, oxidation can lead to the formation of quinones, which are cyclic compounds with two carbonyl groups. The mechanism often involves the formation of a radical intermediate, which can stabilize and rearrange to yield a single product, depending on the substituents on the aromatic ring.

Quinone Formation and Stability

Quinones are highly stable compounds formed from the oxidation of phenols. The stability arises from the delocalization of electrons in the conjugated system of the quinone structure. In cases where a single quinone product is formed, it indicates that the oxidation process leads to a unique arrangement of carbonyl groups that minimizes steric hindrance and maximizes resonance stabilization.

Recommended video:

1:47

Oxidation of Phenols to Quinones Concept 1

Related Practice

Textbook Question

In the second propagation step in the bromination of toluene, Br₂ is only attacked by a radical on the substituent carbon. Why?

views

Textbook Question

Predict the product(s) of the following reactions.

(k)

views

Textbook Question

The benzylic bromide shown undergoes neither S_N1 nor S_N2 substitution reactions. Explain.

views

Textbook Question

Suggest the reagents used to effect the transformations shown.

(c)

views

Textbook Question

Suggest the reagents used to effect the transformations shown.

(a)

views

Textbook Question

When (R)-(1-bromoethyl)benzene is treated with sodium cyanide, a single enantiomer is produced. However, upon treatment of the same molecule with water, a mixture of two enantiomers is obtained.

(a) Explain these results.

(b) Why is only partial racemization sometimes observed?