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Ch.9 - Alkynes
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.9 - AlkynesProblem 8a
Chapter 9, Problem 8a

Show how you would synthesize each compound, beginning with acetylene and any necessary additional reagents
(a)

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1
Step 1: Begin with acetylene (H—C≡C—H) as the starting material. Acetylene is a terminal alkyne, which can undergo nucleophilic substitution reactions when treated with a strong base.
Step 2: Deprotonate acetylene using a strong base such as sodium amide (NaNH₂) to generate the acetylide ion (⁻C≡C—H). This ion is highly nucleophilic and can attack electrophiles.
Step 3: React the acetylide ion with formaldehyde (H₂C=O), which is an electrophilic carbonyl compound. This reaction proceeds via nucleophilic addition, where the acetylide ion attacks the carbonyl carbon of formaldehyde.
Step 4: After the nucleophilic addition, the intermediate formed is protonated using a mild acid (e.g., H₃O⁺) to yield the final product, prop-2-yn-1-ol (H—C≡C—CH₂OH).
Step 5: Verify the structure of the product to ensure it matches the desired compound, prop-2-yn-1-ol, which contains a terminal alkyne group and a hydroxymethyl (-CH₂OH) group.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acetylene as a Building Block

Acetylene (C2H2) is a simple alkyne that serves as a versatile building block in organic synthesis. Its triple bond allows for various reactions, including nucleophilic additions and coupling reactions. Understanding how to manipulate acetylene is crucial for constructing more complex molecules, such as propargyl alcohol.
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Nucleophilic Addition Reactions

Nucleophilic addition reactions involve the attack of a nucleophile on an electrophilic carbon, often found in carbonyl compounds or alkynes. In the synthesis of propargyl alcohol, a nucleophile can add to the terminal carbon of acetylene, leading to the formation of alcohols. Mastery of these reactions is essential for building functionalized organic compounds.
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Functional Group Transformations

Functional group transformations are chemical reactions that convert one functional group into another, allowing for the modification of molecular structures. In synthesizing propargyl alcohol, the transformation of an alkyne to an alcohol involves specific reagents, such as water and a catalyst, to facilitate the addition of hydroxyl groups. Understanding these transformations is key to designing effective synthetic pathways.
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Related Practice
Textbook Question

Solved Problem 9-1 showed the synthesis of dec-3-yne by adding the hexyl group first, then the ethyl group. Show the reagents and intermediates involved in the other order of synthesis of dec-3-yne, by adding the ethyl group first and the hexyl group last.

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Textbook Question

Show how you might synthesize the following compounds, using acetylene and any ­suitable alkyl halides as your starting materials. If the compound given cannot be ­synthesized by this method, explain why.

d. 4-methylhex-2-yne

e. 5-methylhex-2-yne

f. cyclodecyne

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Textbook Question

Show how you would synthesize each compound, beginning with acetylene and any necessary additional reagents

(c)

(d)

655
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Textbook Question

Show how you might synthesize the following compounds, using acetylene and any ­suitable alkyl halides as your starting materials. If the compound given cannot be ­synthesized by this method, explain why.

a. hex-1-yne

b. hex-2-yne

c. hex-3-yne

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Textbook Question

Show how you would synthesize each compound, beginning with acetylene and any necessary additional reagents

(b)

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Textbook Question

Show how you would synthesize 2-phenylhex-3-yn-2-ol, starting with acetophenone (PhCOCH3) and any other reagents you need. ("2-ol" means there is an OH group on C2.)

1287
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