Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 14: Problem 27

2-Methy1-1-phenylpropane yields only 1-bromo-2-methyl-1phenylpropane when treated with \(\mathrm{NBS}\) in \(\mathrm{CCl}_{4}\). Explain.

Short Answer

Expert verified
NBS selectively brominates the benzylic position on 2-Methyl-1-phenylpropane to yield 1-bromo-2-methyl-1-phenylpropane.

Step by step solution

01

Identify the Reactant and Reagent

The reactant is 2-Methyl-1-phenylpropane. The reagent is \( \text{NBS} \) (N-Bromosuccinimide) in \( \text{CCl}_4 \) (carbon tetrachloride).
02

Understand the Mechanism

\( \text{NBS} \) in \( \text{CCl}_4 \) typically undergoes allylic or benzylic bromination. This suggests that bromine will substitute one of the hydrogen atoms in the benzylic or allylic position.
03

Determine the Benzylic Position

In 2-Methyl-1-phenylpropane, the benzylic position is the carbon directly attached to the benzene ring. This is Carbon-1, which is also connected to the methyl group.
04

Reason for Selectivity

The reaction selectively forms 1-bromo-2-methyl-1-phenylpropane because \( \text{NBS} \) prefers to substitute at the benzylic position (Carbon-1), resulting in the most stable benzylic radical intermediate.
05

React by NBS Bromination

NBS replaces one of the hydrogen atoms on the benzylic carbon (Carbon-1), forming the product 1-bromo-2-methyl-1-phenylpropane.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

Key Concepts

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

N-Bromosuccinimide
N-Bromosuccinimide, commonly abbreviated as NBS, is a chemical reagent used in organic synthesis. It is particularly effective for brominating allylic and benzylic positions. NBS is often preferred over elemental bromine due to its selectivity and milder reaction conditions.
NBS reacts in the presence of a radical initiator under conditions that promote the formation of radicals.
In this process, NBS provides a source of bromine radicals that target specific hydrogen atoms in the substrate molecule, leading to the desired brominated product.
Benzylic Position
The benzylic position refers to the carbon atom that is directly attached to a benzene ring. This position is especially reactive due to the stability of the resulting benzylic radical or carbocation intermediates.
In the context of 2-Methyl-1-phenylpropane, the benzylic position is the carbon atom connected to both the benzene ring and the adjacent methyl group.
This location is significant because it allows for the formation of stable radicals, which are crucial for the bromination process facilitated by NBS.
Radical Intermediates
Radical intermediates play a pivotal role in the bromination mechanism with NBS. A radical is a species with an unpaired electron, making it highly reactive.
In the NBS bromination process, the reaction initiates with the formation of a bromine radical. This bromine radical abstracts a hydrogen atom from the benzylic position, generating a benzylic radical.
The benzylic radical is stabilized through resonance by the aromatic ring, which makes this position particularly favorable for radical formation. The stabilized intermediate then reacts with another bromine radical from NBS to form the final brominated product.
Reaction Mechanism
The reaction mechanism for the bromination of 2-Methyl-1-phenylpropane using NBS involves a sequence of radical steps.
Here is a simplified breakdown of the mechanism:
  • Initiation: NBS decomposes to generate a bromine radical and succinimide.
  • Propagation: The bromine radical abstracts a hydrogen atom from the benzylic position, creating a benzylic radical intermediate.
  • The benzylic radical interacts with another molecule of NBS, which supplies a bromine atom to complete the substitution, forming the final brominated product.
This mechanism helps explain why the reaction is selective for the benzylic position, resulting in 1-bromo-2-methyl-1-phenylpropane as the final product.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

One early problem with the Kekulé structure was that only one 1,2 -disubstituted isomer of benzene could be found for any given substituent. That is, there is only one 1,2 -dimethylbenzene (o-xylene). Explain why this observation would have been hard for Kekulé to explain.

The nitronium ion \(\left({ }^{+} \mathrm{NO}_{2}\right)\) is known and can react with simple benzenes to give nitrobenzenes. Write an arrow formalism mechanism for this reaction.

Predict the product of the reaction with \(\mathrm{NBS}\left(\mathrm{CCl}_{4}, b v\right)\) for each of the following compounds: (a) 3 -phenyloctane (b) 3 -methyl-1-phenylbutane (c) \((Z)-1\)-phenyl-2-butene (d) isopropylbenzene (e) phenylcyclohexane

Try to construct an aromatic heterocycle in which there is an oxygen and a nitrogen in a neutral sixmembered ring.

Predict the major product(s), if any, for the bromination \(\left(\mathrm{Br}_{2}, \mathrm{CH}_{2} \mathrm{Cl}_{2}\right)\) of the following compounds: (a) styrene (b) 1-ethyl-3-nitrobenzene (c) \((Z)-2\)-phenyl-2-butene (d) 3 -phenyl-1-propene (e) 3 -phenylheptane
See all solutions

Recommended explanations on Chemistry Textbooks

Chemical Analysis

Read Explanation

Nuclear Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation

Inorganic Chemistry

Read Explanation

Chemical Reactions

Read Explanation

Physical Chemistry

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free