Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions

Problem 44c(ix)

Chapter 9, Problem 44c(ix)

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.
(c)

Verified step by step guidance

Identify the alkyne structure in the given problem. Alkynes are hydrocarbons containing a carbon-carbon triple bond (C≡C). Note that the reaction involves Br₂ (bromine) in 2 equivalents, which means the reaction will proceed in two steps.

Understand the reaction mechanism: When an alkyne reacts with Br₂, the first equivalent of bromine adds across the triple bond, converting it into a dibromoalkene (a double bond with two bromine atoms attached). The second equivalent of bromine then reacts with the dibromoalkene to form a tetrabromoalkane (a single bond with four bromine atoms attached).

Write the reaction for the first equivalent of Br₂: The triple bond (C≡C) undergoes an electrophilic addition reaction with Br₂, forming a trans-dibromoalkene. Represent this intermediate product using the correct chemical structure.

Write the reaction for the second equivalent of Br₂: The trans-dibromoalkene reacts with another molecule of Br₂, resulting in the addition of two more bromine atoms across the double bond. This forms a tetrabromoalkane as the final product. Represent this final product using the correct chemical structure.

If stereochemistry is relevant, ensure that you indicate the stereochemical outcomes (e.g., anti-addition for the first step). If two products are possible due to symmetry or regioselectivity, clearly show both products and explain why they form.

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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 (C≡C). They are unsaturated compounds and are generally more reactive than alkenes and alkanes due to the presence of this triple bond. Understanding the structure and reactivity of alkynes is crucial for predicting the products of chemical reactions involving these compounds.

Electrophilic Addition Reactions

Electrophilic addition reactions occur when an electrophile reacts with a nucleophile, leading to the formation of a more saturated product. In the case of alkynes, the triple bond acts as a nucleophile, allowing electrophiles like bromine (Br₂) to add across the triple bond. This reaction typically results in the formation of dibrominated products when two equivalents of bromine are used.

Regioselectivity and Stereochemistry

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others, while stereochemistry involves the spatial arrangement of atoms in molecules. When alkynes react with bromine, the addition can lead to different products based on how the bromine atoms add to the carbon atoms of the triple bond, resulting in both regioisomers and potential stereoisomers, depending on the reaction conditions.

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Related Practice

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (ii) H₂, Pd/C, Pb(OAc)₂ , CaCO₃ (Lindlar's catalyst). If you expect two products, show both.

(c)

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Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (iii) Na⁰ , NH₃ (liquid), ―33°C . If you expect two products, show both.

(c)

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Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (i) H₂ , Pd/C; If you expect two products, show both.

(c)

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Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (viii) Cl₂ (1 equiv.). If you expect two products, show both.

(c)

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Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (vi) H₂SO₄, HgSO₄, H₂O. If you expect two products, show both.

(c)

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Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (iv) HBr (1 equiv.). If you expect two products, show both.

(c)

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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.(c)

Verified video answer for a similar problem:

Key Concepts

Alkynes

Electrophilic Addition Reactions

Regioselectivity and Stereochemistry

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.
(c)