Textbook Question
When 3-methyl-1-butene reacts with HBr, two alkyl halides are formed: 2-bromo-3-methylbutane and 2-bromo-2-methylbutane. Propose a mechanism that explains the formation of these two products.
10. Addition Reactions
Hydrohalogenation
1:25 minutesProblem 36a
Textbook Question
(a) How would you convert propene to 2-bromopropane?
Verified step by step guidance1
Identify the starting material (propene) and the desired product (2-bromopropane). Propene is an alkene, and the reaction involves adding a bromine atom to the molecule.
Recognize that this is an electrophilic addition reaction, specifically hydrohalogenation, where HBr is used to add a hydrogen atom and a bromine atom across the double bond of the alkene.
Apply Markovnikov's rule to 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 already has more hydrogen atoms, while the bromine atom will add to the carbon with fewer hydrogen atoms.
Write the reaction mechanism: (1) The π electrons of the double bond attack the hydrogen atom of HBr, forming a carbocation intermediate on the more substituted carbon. (2) The bromide ion (Br⁻) then attacks the carbocation, resulting in the formation of 2-bromopropane.
Verify the product structure to ensure that the bromine atom is attached to the second carbon of the original propene molecule, yielding 2-bromopropane as the final product.
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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 propene, the double bond acts as a nucleophile, allowing it to react with an electrophile such as bromine. This process results in the formation of a more stable product, in this case, 2-bromopropane.
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Markovnikov's Rule
Markovnikov's Rule states that when HX (where X is a halogen) is added to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This principle helps predict the major product of the reaction. For propene, this means that bromine will add to the more substituted carbon, leading to the formation of 2-bromopropane.
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Stereochemistry of Addition Reactions
Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the addition of bromine to propene, the stereochemical outcome can lead to different isomers, including enantiomers or diastereomers. Understanding the stereochemical implications is crucial for predicting the properties and reactivity of the resulting 2-bromopropane.
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