Organic Chemistry : Help with Alkyne Synthesis

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Help With Alkyne Synthesis

What is the best reagent for abstracting a hydrogen from ethyne?

Possible Answers:

None of these

Correct answer:

Explanation:

The triple bond in ethyne makes the hydrogens slightly more acidic than those found in ethane. A very strong base, such as the conjugate base of ammonia, would be able to abstract that hydrogen. The abstraction turns the base into ammonia. It also creates a carbanion that can be used for chain extension and alkyne synthesis.

Example Question #2 : Help With Alkyne Synthesis

Untitled

What is the product of the compound when it reacts with two equivalents of base?

Possible Answers:

2-pentyne

1-pentene

None of these

1-pentyne

2-pentene

Correct answer:

2-pentyne

Explanation:

For each equivalent of base, a pi bond is formed between the carbons initially bound to the bromine atoms. For each bond formed, a bromine leaving group leaves the hydrocarbon. One equivalent of base abstracts a hydrogen. The electrons from the bond to the hydrogen create a pi bond. This occurs twice, and a triple bond is formed. The result is a 5-carbon chain with a triple bond between the second and third carbons. This molecule is 2-pentyne.

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