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Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 11 - Properties and Synthesis of Alkyl Halides: Radical ReactionsProblem 22d
Chapter 10, Problem 22d

Predict the major products of the following alkane halogenation reactions. [The number of products shown ignores the formation of racemic mixtures.]
(d) Alkane reacts with Br2 under heat to form one major product in free radical halogenation.

Verified step by step guidance
1
Identify the type of halogenation reaction: Alkane halogenation typically involves the substitution of a hydrogen atom in an alkane with a halogen atom, usually chlorine or bromine, through a radical chain mechanism.
Determine the type of halogen used: The reactivity and selectivity of the halogen (e.g., Cl2 or Br2) will influence the major product. Bromination is more selective than chlorination, often leading to the formation of the most stable radical intermediate.
Identify the most stable radical intermediate: In the radical chain mechanism, the stability of the radical intermediate is crucial. Tertiary radicals are more stable than secondary, which are more stable than primary radicals. Therefore, the hydrogen atom on the carbon that forms the most stable radical is most likely to be substituted.
Consider the reaction conditions: The presence of light or heat is necessary to initiate the radical chain reaction. These conditions help in the homolytic cleavage of the halogen molecule to form radicals.
Predict the major product: Based on the stability of the radical intermediates and the selectivity of the halogen, predict which hydrogen atom will be substituted by the halogen to form the major product. For example, in bromination, the major product will likely result from the substitution at the tertiary carbon if available.

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Key Concepts

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

Alkane Halogenation

Alkane halogenation is a reaction where a halogen, such as chlorine or bromine, replaces a hydrogen atom in an alkane. This process typically involves free radical mechanisms initiated by heat or light, leading to the formation of haloalkanes. Understanding the reactivity and selectivity of different halogens is crucial for predicting the major products.
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Free Radical Mechanism

The free radical mechanism is a chain reaction involving initiation, propagation, and termination steps. In alkane halogenation, radicals are generated when halogen molecules split into atoms under heat or light. These radicals react with alkanes, abstracting hydrogen atoms and forming new radicals, which continue the chain reaction until termination occurs.
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Regioselectivity in Halogenation

Regioselectivity refers to the preference for a chemical reaction to occur at one location over others in a molecule. In alkane halogenation, the most stable radical intermediate determines the major product. Typically, tertiary radicals are more stable than secondary or primary ones, leading to halogenation at the most substituted carbon atom.
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Related Practice
Textbook Question

Predict the major products of the following alkane halogenation reactions. [The number of products shown ignores the formation of racemic mixtures.]

(b)

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Textbook Question

Predict the major products of the following alkane halogenation reactions. [The number of products shown ignores the formation of racemic mixtures.]

(c)

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Textbook Question

Can you make a 1° bromoalkane like (3-bromopropyl)cyclopentane using alkane halogenation? Why or why not?

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Textbook Question

Why is a 2° carbon radical more stable than a 1° carbon radical?

Textbook Question

Predict the major products of the following alkene halogenation reactions. [D is the symbol for deuterium, an isotope of hydrogen.]

(a)

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Textbook Question

Suppose a 2-halobutane was needed for a synthetic sequence. Starting your synthesis with butane, would it be best to put a chlorine or bromine at that position? Explain.

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