Textbook Question
What is the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HCl?
(d)
10. Addition Reactions
Hydrohalogenation
1:49 minutesProblem 61b(i)
Textbook Question
Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (i) HBr;
(b) 
Verified step by step guidance1
Step 1: Identify the structure of the alkene. Alkenes are hydrocarbons containing a carbon-carbon double bond (C=C). The reactivity of the alkene depends on the position and substitution of the double bond.
Step 2: Recall the mechanism of the reaction between an alkene and HBr. This is an electrophilic addition reaction where the π-electrons of the double bond attack the proton (H⁺) from HBr, forming a carbocation intermediate.
Step 3: Determine the stability of the carbocation intermediate. The more substituted the carbocation (tertiary > secondary > primary), the more stable it is. This stability influences the regioselectivity of the reaction.
Step 4: Apply Markovnikov's rule. In the addition of HBr to an alkene, the hydrogen atom (H⁺) will add to the carbon of the double bond that has more hydrogen atoms, while the bromine atom (Br⁻) will add to the carbon with fewer hydrogen atoms.
Step 5: Draw the final product(s) based on the regioselectivity and stereochemistry of the reaction. If the alkene is symmetrical, only one product will form. If the alkene is asymmetrical, consider the possibility of multiple products, including any stereoisomers.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition
Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a nucleophile, typically involving alkenes. In the case of alkenes reacting with HBr, the double bond acts as a nucleophile, attacking the electrophilic hydrogen atom, leading to the formation of a carbocation intermediate. This process is crucial for predicting the products of reactions involving alkenes.
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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 the formation of the more stable carbocation and thus influencing the final product distribution when alkenes react with HBr.
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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 can be classified as primary, secondary, or tertiary based on the number of alkyl groups attached to the positively charged carbon. Tertiary carbocations are the most stable due to hyperconjugation and inductive effects, which play a significant role in determining the product of alkene reactions with electrophiles like HBr.
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