Textbook Question
Draw the product or products that will be obtained from the reaction of cis-2-butene and trans-2-butene with each of the following reagents. If a product can exist as stereoisomers, show which stereoisomers are formed.
1. HCl
10. Addition Reactions
Hydrohalogenation
5:22 minutesProblem 46a
Textbook Question
Predict the major products of the following reactions, and give the structures of any intermediates. Include stereochemistry where appropriate.
(a) 
Verified step by step guidance1
Step 1: Identify the type of reaction. Both reactions involve the addition of a hydrogen halide (HBr or HCl) to an alkene. This is an electrophilic addition reaction, where the π-electrons of the alkene attack the proton (H⁺) from the hydrogen halide.
Step 2: Determine the regioselectivity using Markovnikov's rule. According to Markovnikov's rule, the hydrogen atom from the hydrogen halide will add to the carbon of the double bond that has more hydrogen atoms, while the halide (Br⁻ or Cl⁻) will add to the carbon with fewer hydrogen atoms.
Step 3: Analyze the intermediate. The addition of H⁺ to the alkene forms a carbocation intermediate. The stability of the carbocation is crucial, as more stable carbocations (tertiary > secondary > primary) are favored.
Step 4: Consider stereochemistry. If the reaction generates a chiral center, the product may exist as a racemic mixture (equal amounts of enantiomers) due to the planar nature of the carbocation intermediate.
Step 5: Draw the major product. After the halide ion (Br⁻ or Cl⁻) attacks the carbocation, the major product is formed. Ensure the structure reflects the regioselectivity and stereochemistry of the reaction.
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Key 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 this case, the alkene reacts with HCl, where the double bond acts as a nucleophile, attacking the electrophilic hydrogen atom. This results in the formation of a carbocation intermediate, which is crucial for determining the final product.
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Carbocation Stability
Carbocation stability is a key concept in predicting the products of electrophilic addition reactions. Carbocations are positively charged carbon species that can vary in stability based on their substitution; tertiary carbocations are more stable than secondary or primary ones. The stability of the carbocation formed during the reaction influences the pathway and the major product formed, as more stable intermediates lead to more favorable reactions.
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Stereochemistry in Reactions
Stereochemistry refers to the spatial arrangement of atoms in molecules and is crucial in organic reactions, especially those involving chiral centers. In the context of electrophilic addition, the stereochemistry of the product can be influenced by the formation of the carbocation and the subsequent attack of the nucleophile. Understanding stereochemical outcomes, such as whether the addition is syn or anti, is essential for accurately predicting the structure of the final products.
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