Alkynes & Synthesis

⚗️ Alkynes Synthesis

Part 1 of 7 — Alkyne Structure & Properties

1. Alkynes

C≡C triple bond (sp hybridized, linear)

2. Terminal alkynes

H-C≡C-R

3. Internal alkynes

R-C≡C-R

4. Bond strength

triple > double > single

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Key Concepts Summary

• Alkynes: C≡C triple bond (sp hybridized, linear)
• Terminal alkynes: H-C≡C-R
• Internal alkynes: R-C≡C-R
• Bond strength: triple > double > single

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Alkyne Acidity

Part 2 of 7 — Alkyne Acidity

1. Terminal alkynes are weakly acidic (pKa ~25)

Terminal alkynes are weakly acidic (pKa ~25)

2. NaNH₂ deprotonates terminal alkynes → acetylide anion

NaNH₂ deprotonates terminal alkynes → acetylide anion

3. Acetylide is a good nucleophile and base

Acetylide is a good nucleophile and base

4. Alkylation

R-C≡C⁻ + R'-X → R-C≡C-R' (SN2)

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Key Concepts Summary

• Terminal alkynes are weakly acidic (pKa ~25)
• NaNH₂ deprotonates terminal alkynes → acetylide anion
• Acetylide is a good nucleophile and base
• Alkylation: R-C≡C⁻ + R'-X → R-C≡C-R' (SN2)

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Addition to Alkynes

Part 3 of 7 — Addition to Alkynes

1. HX addition

follows Markovnikov's rule

2. 1 equivalent HX → vinyl halide

1 equivalent HX → vinyl halide

3. 2 equivalents HX → geminal dihalide

2 equivalents HX → geminal dihalide

4. Hydration

H₂O/H⁺/HgSO₄ → ketone (Markovnikov)

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Key Concepts Summary

• HX addition: follows Markovnikov's rule
• 1 equivalent HX → vinyl halide
• 2 equivalents HX → geminal dihalide
• Hydration: H₂O/H⁺/HgSO₄ → ketone (Markovnikov)

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Reduction of Alkynes

Part 4 of 7 — Reduction of Alkynes

1. H₂/Lindlar catalyst → cis-alkene (syn addition, partial reduction)

H₂/Lindlar catalyst → cis-alkene (syn addition, partial reduction)

2. Na/NH₃(l) → trans-alkene (anti addition, dissolving metal)

Na/NH₃(l) → trans-alkene (anti addition, dissolving metal)

3. H₂/Pd → alkane (full reduction)

H₂/Pd → alkane (full reduction)

4. Selective reduction is a powerful synthetic tool

Selective reduction is a powerful synthetic tool

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Key Concepts Summary

• H₂/Lindlar catalyst → cis-alkene (syn addition, partial reduction)
• Na/NH₃(l) → trans-alkene (anti addition, dissolving metal)
• H₂/Pd → alkane (full reduction)
• Selective reduction is a powerful synthetic tool

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Alkyne Synthesis

Part 5 of 7 — Alkyne Synthesis

1. Dehydrohalogenation

2 equivalents of base from dihalide → alkyne

2. Double elimination

geminal or vicinal dihalide → alkyne

3. Acetylide alkylation builds carbon-carbon bonds

Acetylide alkylation builds carbon-carbon bonds

4. Retrosynthetic analysis for alkyne targets

Retrosynthetic analysis for alkyne targets

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Key Concepts Summary

• Dehydrohalogenation: 2 equivalents of base from dihalide → alkyne
• Double elimination: geminal or vicinal dihalide → alkyne
• Acetylide alkylation builds carbon-carbon bonds
• Retrosynthetic analysis for alkyne targets

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Problem-Solving Workshop

Part 6 of 7 — Problem-Solving Workshop

1. Predicting products of alkyne reactions

Predicting products of alkyne reactions

2. Designing syntheses using acetylide chemistry

Designing syntheses using acetylide chemistry

3. Choosing selective reduction conditions

Choosing selective reduction conditions

4. Multi-step synthesis problems

Multi-step synthesis problems

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Key Concepts Summary

• Predicting products of alkyne reactions
• Designing syntheses using acetylide chemistry
• Choosing selective reduction conditions
• Multi-step synthesis problems

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Synthesis & Review

Part 7 of 7 — Synthesis & Review

1. Alkynes are versatile functional groups

Alkynes are versatile functional groups

2. Acetylide alkylation forms C-C bonds

Acetylide alkylation forms C-C bonds

3. Selective reduction gives either cis or trans alkene

Selective reduction gives either cis or trans alkene

4. Review

alkyne reactions and synthesis

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Key Concepts Summary

• Alkynes are versatile functional groups
• Acetylide alkylation forms C-C bonds
• Selective reduction gives either cis or trans alkene
• Review: alkyne reactions and synthesis

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