Textbook Question
Predict the major product(s) of the following allylic bromination reactions.
(b)
11. Radical Reactions
Allylic Bromination
2:30 minutesProblem 31a
Textbook Question
What is the major product of the following reactions? Disregard stereoisomers:
a. 
Verified step by step guidance1
Step 1: Recognize the reagents and reaction conditions. NBS (N-Bromosuccinimide) in the presence of peroxide and heat is commonly used for allylic bromination. This reaction selectively replaces a hydrogen atom at the allylic position (a carbon adjacent to a double bond) with a bromine atom.
Step 2: Identify the allylic positions in the given molecule. The starting material is cyclopentene, which has two allylic positions: one on each carbon adjacent to the double bond.
Step 3: Determine the most reactive allylic position. Both allylic positions in cyclopentene are equivalent due to symmetry, so bromination can occur at either position.
Step 4: Predict the major product. Bromination at the allylic position will result in the formation of 3-bromocyclopentene. Since stereoisomers are disregarded, only the structure of the major product is considered.
Step 5: Understand the mechanism. The reaction proceeds via a radical mechanism initiated by the peroxide and heat. The peroxide generates bromine radicals, which abstract an allylic hydrogen to form an allylic radical. The allylic radical then reacts with bromine to form the brominated product.
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Video duration:
2mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reaction Mechanisms
Understanding reaction mechanisms is crucial in organic chemistry as they describe the step-by-step process by which reactants transform into products. This includes identifying intermediates, transition states, and the types of bonds formed or broken during the reaction. Familiarity with common mechanisms, such as nucleophilic substitution or elimination, helps predict the major products of a reaction.
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Functional Groups
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Recognizing functional groups allows chemists to predict reactivity and the types of reactions that can occur. For example, alcohols, carboxylic acids, and amines each have distinct behaviors in reactions, influencing the final products formed.
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Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to occur at one location over another in a molecule. This concept is essential when predicting the major product of a reaction, as certain pathways may lead to more stable or favorable products based on the structure of the reactants. Understanding regioselectivity helps in determining which isomer will be predominantly formed in a reaction.
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