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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 8b
Chapter 9, Problem 8b

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

Verified step by step guidance
1
Step 1: Begin with acetylene (C≡CH) as the starting material. Perform an alkylation reaction by treating acetylene with sodium amide (NaNH₂) to generate the acetylide ion (C≡C⁻). Then, react the acetylide ion with 1-bromopropane (CH₃CH₂CH₂Br) to introduce the propyl group, forming CH₃CH₂CH₂C≡CH.
Step 2: Perform a second alkylation reaction. Treat the terminal alkyne (CH₃CH₂CH₂C≡CH) with sodium amide (NaNH₂) again to generate the acetylide ion (CH₃CH₂CH₂C≡C⁻). React this ion with methyl iodide (CH₃I) to introduce the methyl group, forming CH₃C≡CCH₂CH₂CH₃.
Step 3: To introduce the hydroxyl group at the 4-position, perform a hydroboration-oxidation reaction. First, treat the alkyne (CH₃C≡CCH₂CH₂CH₃) with disiamylborane (a sterically hindered borane reagent) to selectively add boron to the less substituted carbon of the triple bond. Then, oxidize the organoborane intermediate using hydrogen peroxide (H₂O₂) and sodium hydroxide (NaOH) to form the alcohol group, yielding CH₃C≡CCH(OH)CH₂CH₂CH₃.
Step 4: Verify the structure of the product. The final compound should be hept-2-yn-4-ol, with the hydroxyl group (-OH) attached to the 4th carbon and the triple bond between the 2nd and 3rd carbons.
Step 5: Ensure proper purification and characterization of the product using techniques such as distillation or chromatography, and confirm the structure using spectroscopic methods like NMR and IR.

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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 are characterized by the general formula CnH2n-2. In synthesis, alkynes can undergo various reactions, including addition reactions, which are crucial for forming more complex molecules from simpler starting materials like acetylene.
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Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In the compound hept-2-yn-4-ol, the hydroxyl group (-OH) is a functional group that indicates the presence of an alcohol, influencing the compound's reactivity and properties. Understanding functional groups is essential for predicting the outcomes of chemical reactions.
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Synthesis Pathways

Synthesis pathways refer to the step-by-step methods used to construct complex organic molecules from simpler precursors. In organic chemistry, synthesizing a compound like hept-2-yn-4-ol from acetylene involves a series of reactions, including alkylation and functional group transformations. Mastery of synthesis pathways is vital for designing efficient routes to target compounds.
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Related Practice
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

(a)

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Textbook Question

When 2,2-dibromo-1-phenylpropane is heated overnight in fused KOH at 200 C, the major product is a foul-smelling compound of formula C9H8. Propose a structure for this product, and give a mechanism to account for its formation.

Problem-Solving Hint:

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Textbook Question

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

(c)

(d)

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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 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.)

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