Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions

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

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Mullins 1st Edition

Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions

Problem 34b

Chapter 9, Problem 34b

Predict the alkyne and reactants you might use to make the following haloalkenes. [Providing the reactant and the reagent is how we start thinking about synthesis.]
(b)

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Analyze the target molecule: The product is a haloalkene with a bromine atom attached to a double bond. The structure suggests that the alkyne precursor underwent a selective addition reaction.

Identify the reaction type: To synthesize a haloalkene from an alkyne, a hydrohalogenation reaction is typically used. This involves adding HX (where X is a halogen, such as Br) to the alkyne under controlled conditions to stop at the alkene stage.

Determine the alkyne precursor: The alkyne precursor should have the same carbon skeleton as the product but with a triple bond in place of the double bond. In this case, the alkyne would be 1-cyclohexyl-2-cyclohexylacetylene.

Select the reagent: Use HBr as the reagent for hydrohalogenation. The reaction conditions should be controlled to ensure the addition stops at the alkene stage rather than proceeding to the alkane.

Consider regioselectivity: The Markovnikov rule applies here, meaning the bromine atom will add to the more substituted carbon of the double bond, resulting in the observed product.

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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. They are unsaturated compounds and can undergo various reactions, including addition reactions. Understanding the structure and reactivity of alkynes is crucial for predicting the products of synthetic pathways, such as the formation of haloalkenes.

Haloalkenes

Haloalkenes, or alkyl halides, are alkenes that contain a halogen atom (like bromine) attached to one of the carbon atoms in the double bond. The presence of the halogen influences the reactivity and properties of the compound, making it important to consider when predicting synthesis routes and selecting appropriate reactants.

Synthesis Strategies

Synthesis strategies in organic chemistry involve planning a series of chemical reactions to construct a desired compound from simpler starting materials. This includes identifying the necessary reactants and reagents, as well as understanding the mechanisms of the reactions involved. Effective synthesis requires knowledge of functional group transformations and reaction conditions.

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Related Practice

Textbook Question

For each of the following ketones/aldehydes, indicate whether it is possible to synthesize it from an alkyne as the only compound in good ( > 50%) yield. If so, how would you do it?

(a)

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Textbook Question

The alkyl carbocation is estimated to be 15 kcal/mol more stable than the alkenyl carbocation. If this is also the difference in the energies of the transition state leading to each, what is the expected rate difference?

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Textbook Question

Predict the major products resulting from the addition of one equivalent of HX to the following alkynes.

(b)

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Textbook Question

Draw the ketone(s) you would expect to form by reacting the following alkynes under the conditions of oxymercuration: (a) 6-methyloct-1-yne, (b) 1,10-dicyclohexyldec-5-yne, and (c) 5-phenylhex-2-yne.

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Textbook Question

Predict the alkyne and reactants you might use to make the following haloalkenes. [Providing the reactant and the reagent is how we start thinking about synthesis.]

(a)

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Textbook Question

Draw the ketone(s) you would expect to form by treating the following alkynes under the conditions of hydroboration–oxidation: (a) 6-methyloct-1-yne, (b) 1,10-dicyclohexyldec-5-yne, and (c) 5-phenylhex-2-yne.

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Predict the alkyne and reactants you might use to make the following haloalkenes. [Providing the reactant and the reagent is how we start thinking about synthesis.](b)

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Key Concepts

Alkynes

Haloalkenes

Synthesis Strategies

Predict the alkyne and reactants you might use to make the following haloalkenes. [Providing the reactant and the reagent is how we start thinking about synthesis.]
(b)