Textbook Question
Draw the products of the following reactions. If the products can exist as stereoisomers show what stereoisomers are formed.
h. cis-2-butene + HBr
10. Addition Reactions
Hydrohalogenation
2:35 minutesProblem 17b
Textbook Question
What is the major product obtained from the reaction of HBr with each of the following?
b. 
Verified step by step guidance1
Step 1: Identify the type of reaction. The reaction of HBr with an alkene is an electrophilic addition reaction, where the alkene undergoes protonation followed by the addition of the bromide ion.
Step 2: Determine the regioselectivity of the reaction. According to Markovnikov's rule, the hydrogen atom from HBr will add to the carbon of the double bond that has more hydrogen atoms, while the bromine atom will add to the carbon with fewer hydrogen atoms.
Step 3: Analyze the structure of the alkene. The double bond is located between the terminal carbon and the adjacent carbon in the chain. The terminal carbon has two hydrogen atoms, while the adjacent carbon has only one hydrogen atom.
Step 4: Predict the intermediate formed. The protonation of the double bond will result in the formation of a carbocation. The more stable carbocation will form on the adjacent carbon (secondary carbocation) rather than the terminal carbon (primary carbocation).
Step 5: Add the bromide ion to the carbocation. The bromide ion will attack the positively charged carbon (the carbocation), resulting in the formation of the major product, which is a bromoalkane with the bromine atom attached to the adjacent carbon of the original double bond.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydrohalogenation
Hydrohalogenation is a chemical reaction where an alkene reacts with a hydrogen halide (like HBr) to form an alkyl halide. This reaction typically follows Markovnikov's rule, which states that the hydrogen atom from the hydrogen halide will attach to the carbon with the most hydrogen atoms already attached, leading to the formation of the more stable carbocation intermediate.
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Markovnikov's Rule
Markovnikov's rule is a principle used to predict the outcome of the addition of HX to alkenes. It states that when HX adds to an asymmetric alkene, the hydrogen atom will bond to the carbon with the greater number of hydrogen substituents, while the halide will bond to the carbon with fewer hydrogen substituents. This results in the formation of the more stable product.
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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. Carbocations are stabilized by electron-donating groups and are more stable when they are tertiary (attached to three other carbons) compared to secondary or primary carbocations. The stability of the carbocation formed during hydrohalogenation influences the major product of the reaction.
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