Alkynes & Synthesis - Complete Interactive Lesson
Part 1: Alkyne Structure & Properties
Alkyne Synthesis and Reactions
**Part 1 of 7 — Terminal Alkyne Acidity**
This part focuses on using terminal alkyne pKa to choose deprotonation reagents. The goal is to connect vocabulary, curved-arrow reasoning, and product prediction in one workflow.
### Mechanism vocabulary for this part
- **terminal alkyne**: alkyne bearing acidic proton on sp carbon
- **acetylide anion**: strong nucleophile/base formed by deprotonation
- **SN2 alkylation**: acetylide attacks primary alkyl halide
- **Lindlar catalyst**: poisoned catalyst giving cis alkene from alkyne
### Worked reaction example
A representative transformation uses **NaNH2, liquid NH3**.
1. Identify the governing mechanism: **deprotonates terminal alkyne**.
2. Predict the dominant product pattern: **acetylide nucleophile formed**.
3. Justify with a mechanistic note: requires terminal C-H.
Exam tip: state mechanism class before drawing product. It reduces avoidable regio- and stereochemistry errors.
Mechanism checkpoint (2 questions)
Deep-Dive: Reaction Pattern Table
Use this table as a rapid decision grid.
| Reagents | Conditions / Mechanistic Trigger | Product Pattern | Why it works |
|---|---|---|---|
| NaNH2, liquid NH3 | deprotonates terminal alkyne | acetylide nucleophile formed | requires terminal C-H |
| acetylide + 1° alkyl bromide | SN2 C-C bond formation | chain-extended alkyne | avoid 2°/3° substrates |
| H2, Lindlar | partial syn hydrogenation | cis alkene | stops before alkane |
| Na, NH3(l) | dissolving metal reduction | trans alkene | anti addition pattern |
### Fast interpretation protocol
1. Map reagent set to mechanism family.
2. Apply regio- or stereochemical rule attached to that family.
3. Check whether rearrangement, equilibration, or reversibility changes the major product call.
Input Practice — enter exact chemistry terms
1) Term for: alkyne bearing acidic proton on sp carbon
2) Term for: strong nucleophile/base formed by deprotonation
3) Product pattern expected under NaNH2, liquid NH3
Dropdown matching (3 prompts)
Strategy: Prediction Traps and Exam Techniques
### Common traps in this part
- Acetylide alkylation works best with primary halides due to SN2 constraints.
- Hydration products are usually carbonyls after tautomerization, not stable enols.
- Lindlar and dissolving metal reductions give opposite alkene stereochemistry.
### High-yield exam sequence
1. **Read reagents before substrate details** to classify mechanism class quickly.
2. **Mark the reactive site** (electrophilic carbon, acidic alpha-carbon, benzylic/allylic position, or aromatic position).
3. **Commit to one major-product logic path** before checking answer choices.
4. **Audit stereochemistry and regiochemistry last** so you do not lose points on orientation errors.
### Timing technique
If two options differ only by orientation or placement, spend 10 seconds restating the governing rule out loud (Markovnikov, anti addition, kinetic control, etc.) before selecting.
Applied synthesis/mechanism check (2 questions)
Part 2: Alkyne Acidity
Alkyne Synthesis and Reactions
**Part 2 of 7 — Acetylide Formation and Alkylation**
This part focuses on forming carbon-carbon bonds with acetylide nucleophiles. The goal is to connect vocabulary, curved-arrow reasoning, and product prediction in one workflow.
### Mechanism vocabulary for this part
- **acetylide anion**: strong nucleophile/base formed by deprotonation
- **SN2 alkylation**: acetylide attacks primary alkyl halide
- **Lindlar catalyst**: poisoned catalyst giving cis alkene from alkyne
- **dissolving metal reduction**: Na/NH3 gives trans alkene from alkyne
### Worked reaction example
A representative transformation uses **acetylide + 1° alkyl bromide**.
1. Identify the governing mechanism: **SN2 C-C bond formation**.
2. Predict the dominant product pattern: **chain-extended alkyne**.
3. Justify with a mechanistic note: avoid 2°/3° substrates.
Exam tip: state mechanism class before drawing product. It reduces avoidable regio- and stereochemistry errors.
Mechanism checkpoint (2 questions)
Deep-Dive: Reaction Pattern Table
Use this table as a rapid decision grid.
| Reagents | Conditions / Mechanistic Trigger | Product Pattern | Why it works |
|---|---|---|---|
| acetylide + 1° alkyl bromide | SN2 C-C bond formation | chain-extended alkyne | avoid 2°/3° substrates |
| H2, Lindlar | partial syn hydrogenation | cis alkene | stops before alkane |
| Na, NH3(l) | dissolving metal reduction | trans alkene | anti addition pattern |
| HgSO4, H2SO4, H2O | Markovnikov hydration | ketone after tautomerization | enol not isolated |
### Fast interpretation protocol
1. Map reagent set to mechanism family.
2. Apply regio- or stereochemical rule attached to that family.
3. Check whether rearrangement, equilibration, or reversibility changes the major product call.
Input Practice — enter exact chemistry terms
1) Term for: strong nucleophile/base formed by deprotonation
2) Term for: acetylide attacks primary alkyl halide
3) Product pattern expected under acetylide + 1° alkyl bromide
Dropdown matching (3 prompts)
Strategy: Prediction Traps and Exam Techniques
### Common traps in this part
- Hydration products are usually carbonyls after tautomerization, not stable enols.
- Lindlar and dissolving metal reductions give opposite alkene stereochemistry.
- Terminal alkyne acidity is stronger than alkene/alkane C-H but still needs strong base.
### High-yield exam sequence
1. **Read reagents before substrate details** to classify mechanism class quickly.
2. **Mark the reactive site** (electrophilic carbon, acidic alpha-carbon, benzylic/allylic position, or aromatic position).
3. **Commit to one major-product logic path** before checking answer choices.
4. **Audit stereochemistry and regiochemistry last** so you do not lose points on orientation errors.
### Timing technique
If two options differ only by orientation or placement, spend 10 seconds restating the governing rule out loud (Markovnikov, anti addition, kinetic control, etc.) before selecting.
Applied synthesis/mechanism check (2 questions)
Part 3: Addition to Alkynes
Alkyne Synthesis and Reactions
**Part 3 of 7 — Partial Hydrogenation Control**
This part focuses on stopping reduction at alkene rather than alkane. The goal is to connect vocabulary, curved-arrow reasoning, and product prediction in one workflow.
### Mechanism vocabulary for this part
- **SN2 alkylation**: acetylide attacks primary alkyl halide
- **Lindlar catalyst**: poisoned catalyst giving cis alkene from alkyne
- **dissolving metal reduction**: Na/NH3 gives trans alkene from alkyne
- **tautomerization**: enol rearranges to carbonyl form
### Worked reaction example
A representative transformation uses **H2, Lindlar**.
1. Identify the governing mechanism: **partial syn hydrogenation**.
2. Predict the dominant product pattern: **cis alkene**.
3. Justify with a mechanistic note: stops before alkane.
Exam tip: state mechanism class before drawing product. It reduces avoidable regio- and stereochemistry errors.
Mechanism checkpoint (2 questions)
Deep-Dive: Reaction Pattern Table
Use this table as a rapid decision grid.
| Reagents | Conditions / Mechanistic Trigger | Product Pattern | Why it works |
|---|---|---|---|
| H2, Lindlar | partial syn hydrogenation | cis alkene | stops before alkane |
| Na, NH3(l) | dissolving metal reduction | trans alkene | anti addition pattern |
| HgSO4, H2SO4, H2O | Markovnikov hydration | ketone after tautomerization | enol not isolated |
| BH3 then H2O2/NaOH | anti-Markovnikov hydration | aldehyde from terminal alkyne | via enol tautomerization |
### Fast interpretation protocol
1. Map reagent set to mechanism family.
2. Apply regio- or stereochemical rule attached to that family.
3. Check whether rearrangement, equilibration, or reversibility changes the major product call.
Input Practice — enter exact chemistry terms
1) Term for: acetylide attacks primary alkyl halide
2) Term for: poisoned catalyst giving cis alkene from alkyne
3) Product pattern expected under H2, Lindlar
Dropdown matching (3 prompts)
Strategy: Prediction Traps and Exam Techniques
### Common traps in this part
- Lindlar and dissolving metal reductions give opposite alkene stereochemistry.
- Terminal alkyne acidity is stronger than alkene/alkane C-H but still needs strong base.
- Acetylide alkylation works best with primary halides due to SN2 constraints.
### High-yield exam sequence
1. **Read reagents before substrate details** to classify mechanism class quickly.
2. **Mark the reactive site** (electrophilic carbon, acidic alpha-carbon, benzylic/allylic position, or aromatic position).
3. **Commit to one major-product logic path** before checking answer choices.
4. **Audit stereochemistry and regiochemistry last** so you do not lose points on orientation errors.
### Timing technique
If two options differ only by orientation or placement, spend 10 seconds restating the governing rule out loud (Markovnikov, anti addition, kinetic control, etc.) before selecting.
Applied synthesis/mechanism check (2 questions)
Part 4: Reduction of Alkynes
Alkyne Synthesis and Reactions
**Part 4 of 7 — Hydration Pathways**
This part focuses on predicting ketone vs aldehyde outcomes after hydration. The goal is to connect vocabulary, curved-arrow reasoning, and product prediction in one workflow.
### Mechanism vocabulary for this part
- **Lindlar catalyst**: poisoned catalyst giving cis alkene from alkyne
- **dissolving metal reduction**: Na/NH3 gives trans alkene from alkyne
- **tautomerization**: enol rearranges to carbonyl form
- **hydration**: adds water equivalent across triple bond
### Worked reaction example
A representative transformation uses **Na, NH3(l)**.
1. Identify the governing mechanism: **dissolving metal reduction**.
2. Predict the dominant product pattern: **trans alkene**.
3. Justify with a mechanistic note: anti addition pattern.
Exam tip: state mechanism class before drawing product. It reduces avoidable regio- and stereochemistry errors.
Mechanism checkpoint (2 questions)
Deep-Dive: Reaction Pattern Table
Use this table as a rapid decision grid.
| Reagents | Conditions / Mechanistic Trigger | Product Pattern | Why it works |
|---|---|---|---|
| Na, NH3(l) | dissolving metal reduction | trans alkene | anti addition pattern |
| HgSO4, H2SO4, H2O | Markovnikov hydration | ketone after tautomerization | enol not isolated |
| BH3 then H2O2/NaOH | anti-Markovnikov hydration | aldehyde from terminal alkyne | via enol tautomerization |
| NaNH2, liquid NH3 | deprotonates terminal alkyne | acetylide nucleophile formed | requires terminal C-H |
### Fast interpretation protocol
1. Map reagent set to mechanism family.
2. Apply regio- or stereochemical rule attached to that family.
3. Check whether rearrangement, equilibration, or reversibility changes the major product call.
Input Practice — enter exact chemistry terms
1) Term for: poisoned catalyst giving cis alkene from alkyne
2) Term for: Na/NH3 gives trans alkene from alkyne
3) Product pattern expected under Na, NH3(l)
Dropdown matching (3 prompts)
Strategy: Prediction Traps and Exam Techniques
### Common traps in this part
- Terminal alkyne acidity is stronger than alkene/alkane C-H but still needs strong base.
- Acetylide alkylation works best with primary halides due to SN2 constraints.
- Hydration products are usually carbonyls after tautomerization, not stable enols.
### High-yield exam sequence
1. **Read reagents before substrate details** to classify mechanism class quickly.
2. **Mark the reactive site** (electrophilic carbon, acidic alpha-carbon, benzylic/allylic position, or aromatic position).
3. **Commit to one major-product logic path** before checking answer choices.
4. **Audit stereochemistry and regiochemistry last** so you do not lose points on orientation errors.
### Timing technique
If two options differ only by orientation or placement, spend 10 seconds restating the governing rule out loud (Markovnikov, anti addition, kinetic control, etc.) before selecting.
Applied synthesis/mechanism check (2 questions)
Part 5: Alkyne Synthesis
Alkyne Synthesis and Reactions
**Part 5 of 7 — Oxidative Cleavage of Alkynes**
This part focuses on interpreting cleavage fragments for structure assignment. The goal is to connect vocabulary, curved-arrow reasoning, and product prediction in one workflow.
### Mechanism vocabulary for this part
- **dissolving metal reduction**: Na/NH3 gives trans alkene from alkyne
- **tautomerization**: enol rearranges to carbonyl form
- **hydration**: adds water equivalent across triple bond
- **hydroboration-oxidation**: anti-Markovnikov hydration path for terminal alkynes
### Worked reaction example
A representative transformation uses **HgSO4, H2SO4, H2O**.
1. Identify the governing mechanism: **Markovnikov hydration**.
2. Predict the dominant product pattern: **ketone after tautomerization**.
3. Justify with a mechanistic note: enol not isolated.
Exam tip: state mechanism class before drawing product. It reduces avoidable regio- and stereochemistry errors.
Mechanism checkpoint (2 questions)
Deep-Dive: Reaction Pattern Table
Use this table as a rapid decision grid.
| Reagents | Conditions / Mechanistic Trigger | Product Pattern | Why it works |
|---|---|---|---|
| HgSO4, H2SO4, H2O | Markovnikov hydration | ketone after tautomerization | enol not isolated |
| BH3 then H2O2/NaOH | anti-Markovnikov hydration | aldehyde from terminal alkyne | via enol tautomerization |
| NaNH2, liquid NH3 | deprotonates terminal alkyne | acetylide nucleophile formed | requires terminal C-H |
| acetylide + 1° alkyl bromide | SN2 C-C bond formation | chain-extended alkyne | avoid 2°/3° substrates |
### Fast interpretation protocol
1. Map reagent set to mechanism family.
2. Apply regio- or stereochemical rule attached to that family.
3. Check whether rearrangement, equilibration, or reversibility changes the major product call.
Input Practice — enter exact chemistry terms
1) Term for: Na/NH3 gives trans alkene from alkyne
2) Term for: enol rearranges to carbonyl form
3) Product pattern expected under HgSO4, H2SO4, H2O
Dropdown matching (3 prompts)
Strategy: Prediction Traps and Exam Techniques
### Common traps in this part
- Acetylide alkylation works best with primary halides due to SN2 constraints.
- Hydration products are usually carbonyls after tautomerization, not stable enols.
- Lindlar and dissolving metal reductions give opposite alkene stereochemistry.
### High-yield exam sequence
1. **Read reagents before substrate details** to classify mechanism class quickly.
2. **Mark the reactive site** (electrophilic carbon, acidic alpha-carbon, benzylic/allylic position, or aromatic position).
3. **Commit to one major-product logic path** before checking answer choices.
4. **Audit stereochemistry and regiochemistry last** so you do not lose points on orientation errors.
### Timing technique
If two options differ only by orientation or placement, spend 10 seconds restating the governing rule out loud (Markovnikov, anti addition, kinetic control, etc.) before selecting.
Applied synthesis/mechanism check (2 questions)
Part 6: Problem-Solving Workshop
Alkyne Synthesis and Reactions
**Part 6 of 7 — Route Design from Alkynes**
This part focuses on planning shortest route to substituted carbonyl compounds. The goal is to connect vocabulary, curved-arrow reasoning, and product prediction in one workflow.
### Mechanism vocabulary for this part
- **tautomerization**: enol rearranges to carbonyl form
- **hydration**: adds water equivalent across triple bond
- **hydroboration-oxidation**: anti-Markovnikov hydration path for terminal alkynes
- **oxidative cleavage**: strong oxidation splits alkyne to carboxyl products
### Worked reaction example
A representative transformation uses **BH3 then H2O2/NaOH**.
1. Identify the governing mechanism: **anti-Markovnikov hydration**.
2. Predict the dominant product pattern: **aldehyde from terminal alkyne**.
3. Justify with a mechanistic note: via enol tautomerization.
Exam tip: state mechanism class before drawing product. It reduces avoidable regio- and stereochemistry errors.
Mechanism checkpoint (2 questions)
Deep-Dive: Reaction Pattern Table
Use this table as a rapid decision grid.
| Reagents | Conditions / Mechanistic Trigger | Product Pattern | Why it works |
|---|---|---|---|
| BH3 then H2O2/NaOH | anti-Markovnikov hydration | aldehyde from terminal alkyne | via enol tautomerization |
| NaNH2, liquid NH3 | deprotonates terminal alkyne | acetylide nucleophile formed | requires terminal C-H |
| acetylide + 1° alkyl bromide | SN2 C-C bond formation | chain-extended alkyne | avoid 2°/3° substrates |
| H2, Lindlar | partial syn hydrogenation | cis alkene | stops before alkane |
### Fast interpretation protocol
1. Map reagent set to mechanism family.
2. Apply regio- or stereochemical rule attached to that family.
3. Check whether rearrangement, equilibration, or reversibility changes the major product call.
Input Practice — enter exact chemistry terms
1) Term for: enol rearranges to carbonyl form
2) Term for: adds water equivalent across triple bond
3) Product pattern expected under BH3 then H2O2/NaOH
Dropdown matching (3 prompts)
Strategy: Prediction Traps and Exam Techniques
### Common traps in this part
- Hydration products are usually carbonyls after tautomerization, not stable enols.
- Lindlar and dissolving metal reductions give opposite alkene stereochemistry.
- Terminal alkyne acidity is stronger than alkene/alkane C-H but still needs strong base.
### High-yield exam sequence
1. **Read reagents before substrate details** to classify mechanism class quickly.
2. **Mark the reactive site** (electrophilic carbon, acidic alpha-carbon, benzylic/allylic position, or aromatic position).
3. **Commit to one major-product logic path** before checking answer choices.
4. **Audit stereochemistry and regiochemistry last** so you do not lose points on orientation errors.
### Timing technique
If two options differ only by orientation or placement, spend 10 seconds restating the governing rule out loud (Markovnikov, anti addition, kinetic control, etc.) before selecting.
Applied synthesis/mechanism check (2 questions)
Part 7: Synthesis & Review
Alkyne Synthesis and Reactions
**Part 7 of 7 — Mixed Reagent Synthesis Review**
This part focuses on integrating alkyne logic with alkene and carbonyl chemistry. The goal is to connect vocabulary, curved-arrow reasoning, and product prediction in one workflow.
### Mechanism vocabulary for this part
- **hydration**: adds water equivalent across triple bond
- **hydroboration-oxidation**: anti-Markovnikov hydration path for terminal alkynes
- **oxidative cleavage**: strong oxidation splits alkyne to carboxyl products
- **terminal alkyne**: alkyne bearing acidic proton on sp carbon
### Worked reaction example
A representative transformation uses **NaNH2, liquid NH3**.
1. Identify the governing mechanism: **deprotonates terminal alkyne**.
2. Predict the dominant product pattern: **acetylide nucleophile formed**.
3. Justify with a mechanistic note: requires terminal C-H.
Exam tip: state mechanism class before drawing product. It reduces avoidable regio- and stereochemistry errors.
Mechanism checkpoint (2 questions)
Deep-Dive: Reaction Pattern Table
Use this table as a rapid decision grid.
| Reagents | Conditions / Mechanistic Trigger | Product Pattern | Why it works |
|---|---|---|---|
| NaNH2, liquid NH3 | deprotonates terminal alkyne | acetylide nucleophile formed | requires terminal C-H |
| acetylide + 1° alkyl bromide | SN2 C-C bond formation | chain-extended alkyne | avoid 2°/3° substrates |
| H2, Lindlar | partial syn hydrogenation | cis alkene | stops before alkane |
| Na, NH3(l) | dissolving metal reduction | trans alkene | anti addition pattern |
### Fast interpretation protocol
1. Map reagent set to mechanism family.
2. Apply regio- or stereochemical rule attached to that family.
3. Check whether rearrangement, equilibration, or reversibility changes the major product call.
Input Practice — enter exact chemistry terms
1) Term for: adds water equivalent across triple bond
2) Term for: anti-Markovnikov hydration path for terminal alkynes
3) Product pattern expected under NaNH2, liquid NH3
Dropdown matching (3 prompts)
Strategy: Prediction Traps and Exam Techniques
### Common traps in this part
- Lindlar and dissolving metal reductions give opposite alkene stereochemistry.
- Terminal alkyne acidity is stronger than alkene/alkane C-H but still needs strong base.
- Acetylide alkylation works best with primary halides due to SN2 constraints.
### High-yield exam sequence
1. **Read reagents before substrate details** to classify mechanism class quickly.
2. **Mark the reactive site** (electrophilic carbon, acidic alpha-carbon, benzylic/allylic position, or aromatic position).
3. **Commit to one major-product logic path** before checking answer choices.
4. **Audit stereochemistry and regiochemistry last** so you do not lose points on orientation errors.
### Timing technique
If two options differ only by orientation or placement, spend 10 seconds restating the governing rule out loud (Markovnikov, anti addition, kinetic control, etc.) before selecting.
Applied synthesis/mechanism check (2 questions)