Textbook Question
Drawing on what you know about the stereochemistry of alkene addition reactions,
b. predict the configuration of the product of the reaction.
817
views
10. Addition Reactions
Alkyne Halogenation
Problem 44f(ix)
Textbook Question
For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (ix) Br2 (2 equiv.). If you expect two products, show both.
(f) 
Verified step by step guidance1
Step 1: Analyze the structure of the alkyne provided in the image. The molecule contains a terminal alkyne group (-C≡CH) attached to a complex cyclic structure with a nitrogen atom and a ketone functional group.
Step 2: Understand the reaction conditions. The treatment with Br₂ (2 equivalents) indicates that the alkyne will undergo halogenation. In this reaction, bromine molecules will add across the triple bond of the alkyne.
Step 3: Predict the first addition of Br₂. The triple bond will react with one equivalent of Br₂, resulting in the formation of a dibromoalkene intermediate. The bromine atoms will add anti to each other due to the mechanism of halogenation.
Step 4: Predict the second addition of Br₂. The dibromoalkene intermediate will react with the second equivalent of Br₂, leading to the formation of a tetrabromoalkane. The bromine atoms will add across the double bond, resulting in a saturated carbon chain with four bromine atoms.
Step 5: Consider stereochemistry and regioselectivity. Since the alkyne is terminal, the addition of bromine will occur without regioselectivity concerns. The stereochemistry of the final product will depend on the anti-addition mechanism during each step of halogenation.
Verified video answer for a similar problem:This video solution was recommended by our tutors as helpful for the problem above
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alkynes
Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. They are unsaturated compounds and are characterized by the general formula CnH2n-2. The presence of the triple bond significantly influences their reactivity, making them more reactive than alkenes and alkanes. Understanding the structure and reactivity of alkynes is crucial for predicting the products of chemical reactions involving these compounds.
Recommended video:
Guided course
09:11
Alkyne Hydration
Electrophilic Addition Reactions
Electrophilic addition reactions are a key type of reaction for unsaturated hydrocarbons, including alkynes. In these reactions, an electrophile reacts with the nucleophilic π bond of the alkyne, leading to the formation of new σ bonds. When treated with bromine (Br₂), for example, alkynes can undergo addition to form dibrominated products. Recognizing the mechanism of these reactions is essential for predicting the products formed under specific conditions.
Recommended video:
Guided course
05:39Features of Addition Mechanisms.
Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In the case of alkynes reacting with bromine, the addition can occur at different positions, leading to different products. Understanding regioselectivity helps in predicting which isomer will be formed based on the stability of intermediates and the nature of the reactants involved.
Recommended video:
Guided course
05:09Heck Reaction
Related Videos
Related Practice