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Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 10 - Alkynes: Electrophilic Addition and Redox ReactionsProblem 34a
Chapter 9, Problem 34a

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) Diagram showing a reaction scheme with empty boxes for reactants leading to a haloalkene product with a bromine atom.

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1
Analyze the given haloalkene structure to determine the position of the halogen atom and the double bond. This will help identify the alkyne precursor and the reaction pathway.
Recall that haloalkenes can be synthesized from alkynes through hydrohalogenation reactions. In this reaction, an alkyne reacts with a hydrogen halide (e.g., HCl, HBr) to form a haloalkene.
Determine the regioselectivity of the reaction. If the reaction follows Markovnikov's rule, the halogen will add to the more substituted carbon of the double bond. If anti-Markovnikov addition is required, a peroxide (e.g., ROOR) is used as a catalyst.
Identify the alkyne that would lead to the given haloalkene. The alkyne should have a triple bond in the position that allows the addition of the hydrogen halide to produce the desired product.
Write the reaction mechanism, showing the addition of the hydrogen halide to the alkyne. Ensure that the intermediate and final product match the structure of the given haloalkene.

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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 participate in various chemical reactions, including addition reactions. Understanding the structure and reactivity of alkynes is crucial for predicting the products of synthetic pathways involving haloalkenes.
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Haloalkenes

Haloalkenes, or alkyl halides, are alkenes that contain one or more halogen atoms (such as chlorine, bromine, or iodine) attached to the carbon skeleton. Their reactivity is influenced by the presence of the halogen, which can participate in nucleophilic substitution or elimination reactions. Recognizing how haloalkenes can be synthesized from alkynes is essential for solving the synthesis question.

Synthesis Pathways

Synthesis pathways refer to the step-by-step methods used to construct complex molecules from simpler ones. In organic chemistry, understanding the various reactions, such as elimination and addition, is vital for predicting how to convert alkynes into haloalkenes. Familiarity with common reagents and reaction conditions is necessary for effective synthesis planning.
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Related Practice
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

We have studied the following reactions in previous chapters. For each, (i) indicate which reaction sheets they should appear on, (ii) show the best structure to use to represent them, and (iii) write the notes you could put in the margin so that the mechanism is implied.

(b) Radical halogenation of an alkane

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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.]

(b)

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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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