Textbook Question
What is the major product obtained from the addition of HBr to each of the following compounds?
a.
b.
10. Addition Reactions
Hydrohalogenation
5:00 minutesProblem 84c,d
Textbook Question
What is the major product of the reaction of each of the following with HBr?
c. 
d. 
Verified step by step guidance1
Step 1: Analyze the structure of the given compounds. Both structures contain alkenes, which are reactive towards HBr via electrophilic addition. The first structure has a branched alkene, while the second structure has a cyclopentane ring with an alkene side chain.
Step 2: Recall the mechanism of electrophilic addition of HBr to alkenes. The reaction proceeds via the formation of a carbocation intermediate. The regioselectivity follows Markovnikov's rule, where the hydrogen atom from HBr adds to the carbon of the double bond with more hydrogens, and the bromine adds to the carbon with fewer hydrogens.
Step 3: For the first structure, identify the double bond and determine the more substituted carbon. The carbocation will form on the more substituted carbon after the hydrogen adds to the less substituted carbon.
Step 4: For the second structure, focus on the alkene side chain. Apply Markovnikov's rule to determine the major product. The hydrogen will add to the terminal carbon of the double bond, forming a carbocation on the adjacent carbon, which is more stable due to hyperconjugation and inductive effects.
Step 5: Consider any possible rearrangements of the carbocation intermediates for both structures. If a more stable carbocation can form via hydride or alkyl shifts, the reaction may proceed through that pathway before bromine adds to the carbocation to form the final product.
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Video duration:
5mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition Reactions
Electrophilic addition reactions are a fundamental type of reaction in organic chemistry where an electrophile reacts with a nucleophile, typically involving alkenes or alkynes. In the presence of HBr, the double or triple bond of the hydrocarbon acts as a nucleophile, attacking the electrophilic hydrogen atom, leading to the formation of a more stable product. Understanding this mechanism is crucial for predicting the major product formed in such reactions.
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Features of Addition Mechanisms.
Markovnikov's Rule
Markovnikov's Rule states that in the addition of HX (where X is a halogen) to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This rule helps predict the regioselectivity of the reaction, guiding chemists in determining which product will be the major one when HBr reacts with unsymmetrical alkenes.
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Carbocation Stability
Carbocation stability is a key concept in organic chemistry that refers to the relative stability of positively charged carbon species. The stability of a carbocation increases with the number of alkyl groups attached to the positively charged carbon, as these groups can donate electron density through inductive effects and hyperconjugation. This concept is essential for predicting the pathway and major product of reactions involving HBr, as the formation of more stable carbocations often leads to the favored product.
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