Q5. Synthesize 1-hexanol starting from acetylene and using alkyl halides containing 4 or fewer carbons and any necessary inorganic reagents.

Background

Topic: Multi-step Organic Synthesis (Alkyne Chemistry, Alkylation, Hydroboration-Oxidation)

This question tests your ability to design a forward synthesis for a target molecule (1-hexanol) starting from a simple alkyne (acetylene), using carbon chain extension and functional group transformations. You must use alkyl halides with four or fewer carbons and appropriate inorganic reagents.

Key Terms and Reactions:

• Acetylene (ethyne): A two-carbon alkyne ().

• Alkylation of terminal alkynes: Using strong base (e.g., ) to deprotonate acetylene, followed by reaction with an alkyl halide to extend the carbon chain.

• Lindlar's catalyst: Used for partial hydrogenation of alkynes to cis-alkenes.

• Hydroboration-oxidation: Converts alkenes to alcohols with anti-Markovnikov selectivity.

Key Formulas and Mechanisms:

• (alkylation)

Step-by-Step Guidance

1. Start with acetylene (). Use sodium amide () to deprotonate the terminal alkyne, generating the acetylide ion ().

2. React the acetylide ion with an appropriate alkyl halide (e.g., ) to extend the carbon chain. This step forms a longer alkyne ().

3. Perform partial hydrogenation of the alkyne using Lindlar's catalyst and hydrogen () to convert the triple bond to a cis-alkene.

4. Apply hydroboration-oxidation ( in THF, followed by and ) to convert the alkene to the alcohol, specifically 1-hexanol.

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