Conjugated Systems & Dienes

⚗️ Conjugated Systems Dienes

Part 1 of 7 — Conjugation & Stability

1. Conjugated dienes

alternating single and double bonds

2. Conjugation stabilizes molecules through delocalization

Conjugation stabilizes molecules through delocalization

3. s-cis and s-trans conformations

s-cis and s-trans conformations

4. Conjugated dienes are more stable than isolated dienes

Conjugated dienes are more stable than isolated dienes

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Key Concepts Summary

• Conjugated dienes: alternating single and double bonds
• Conjugation stabilizes molecules through delocalization
• s-cis and s-trans conformations
• Conjugated dienes are more stable than isolated dienes

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1,2- vs 1,4-Addition

Part 2 of 7 — 1,2- vs 1,4-Addition

1. 1,2-addition

electrophile adds across one double bond (kinetic product)

2. 1,4-addition

electrophile adds across entire system (thermodynamic product)

3. Low temperature favors kinetic (1,2) product

Low temperature favors kinetic (1,2) product

4. High temperature favors thermodynamic (1,4) product

High temperature favors thermodynamic (1,4) product

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Key Concepts Summary

• 1,2-addition: electrophile adds across one double bond (kinetic product)
• 1,4-addition: electrophile adds across entire system (thermodynamic product)
• Low temperature favors kinetic (1,2) product
• High temperature favors thermodynamic (1,4) product

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Diels-Alder Reaction

Part 3 of 7 — Diels-Alder Reaction

1. Diels-Alder

diene + dienophile → cyclohexene (pericyclic)

2. Concerted, one-step, stereospecific

Concerted, one-step, stereospecific

3. Diene must be in s-cis conformation

Diene must be in s-cis conformation

4. Electron-rich diene + electron-poor dienophile → fastest reaction

Electron-rich diene + electron-poor dienophile → fastest reaction

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Key Concepts Summary

• Diels-Alder: diene + dienophile → cyclohexene (pericyclic)
• Concerted, one-step, stereospecific
• Diene must be in s-cis conformation
• Electron-rich diene + electron-poor dienophile → fastest reaction

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Molecular Orbital Theory of Dienes

Part 4 of 7 — Molecular Orbital Theory of Dienes

1. Conjugation extends π system across multiple atoms

Conjugation extends π system across multiple atoms

2. HOMO of diene interacts with LUMO of dienophile

HOMO of diene interacts with LUMO of dienophile

3. Symmetry-allowed thermal [4+2] cycloaddition

Symmetry-allowed thermal [4+2] cycloaddition

4. Frontier molecular orbital theory explains selectivity

Frontier molecular orbital theory explains selectivity

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Key Concepts Summary

• Conjugation extends π system across multiple atoms
• HOMO of diene interacts with LUMO of dienophile
• Symmetry-allowed thermal [4+2] cycloaddition
• Frontier molecular orbital theory explains selectivity

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UV-Vis Spectroscopy

Part 5 of 7 — UV-Vis Spectroscopy

1. UV-Vis spectroscopy

measures π → π* transitions

2. λmax increases with more conjugation

λmax increases with more conjugation

3. Colored compounds absorb visible light

Colored compounds absorb visible light

4. Used to determine extent of conjugation

Used to determine extent of conjugation

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Key Concepts Summary

• UV-Vis spectroscopy: measures π → π* transitions
• λmax increases with more conjugation
• Colored compounds absorb visible light
• Used to determine extent of conjugation

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Problem-Solving Workshop

Part 6 of 7 — Problem-Solving Workshop

1. Drawing Diels-Alder products

Drawing Diels-Alder products

2. Predicting kinetic vs thermodynamic products

Predicting kinetic vs thermodynamic products

3. Retrosynthetic analysis using Diels-Alder

Retrosynthetic analysis using Diels-Alder

4. Interpreting UV-Vis spectra

Interpreting UV-Vis spectra

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Key Concepts Summary

• Drawing Diels-Alder products
• Predicting kinetic vs thermodynamic products
• Retrosynthetic analysis using Diels-Alder
• Interpreting UV-Vis spectra

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Synthesis & Review

Part 7 of 7 — Synthesis & Review

1. Conjugation is key to reactivity and color

Conjugation is key to reactivity and color

2. Diels-Alder is a powerful ring-forming reaction

Diels-Alder is a powerful ring-forming reaction

3. Kinetic vs thermodynamic control is a major theme

Kinetic vs thermodynamic control is a major theme

4. Review

conjugated systems and pericyclic reactions

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Key Concepts Summary

• Conjugation is key to reactivity and color
• Diels-Alder is a powerful ring-forming reaction
• Kinetic vs thermodynamic control is a major theme
• Review: conjugated systems and pericyclic reactions

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