Chapter 18, Problem 18.68P

Interpretation Introduction

(a)

Interpretation:

The complete, detailed mechanism and the major organic product for the given reaction is to be drawn.

Concept introduction:

When ketone is treated with a strong base like LDA, the product enolate anion is formed. In Step 1, LDA deprotonates the $\text{α}$ carbon to yield an enolate anion. The LDA produces kinetic (less substituted) enolate anion. In Step 2, the newly formed enolate anion, which is nucleophilic at the $\text{α}$ carbon, attacks the other given molecule of the aldehyde. The immediate product is an alkoxide anion (${\text{RO}}^{\text{-}}$), which is subsequently protonated in Step 3. The condensation occurs without heat owing to the extended conjugation with aromatic ring in an $\text{α,β -unsaturated}$ carbonyl compound. The dehydration occurs and water is eliminated from the $\text{β -hydroxycarbonyl}$ compound giving the overall product a $\text{C=C}$ double bond. This reaction is called crossed aldol reaction. The dehydration of $\text{β -hydroxycarbonyl}$ compound takes place by proton transfer step followed by heterolysis step and the ${\text{HO}}^{\text{-}}$ leaving group departs to yield the overall product.

Answer to Problem 18.68P

The complete, detailed mechanism and the major organic product for the given reaction is as shown below:

Explanation of Solution

The given reaction is as shown below:

The given reaction is a crossed aldol condensation as the nucleophilic species is generated from a different ketone than the one that is attacked. Firstly, the given ketone is treated with LDA to produce $\text{β -hydroxycarbonyl}$ compound (an aldol ). In Step 1, base LDA deprotonates the $\text{α}$ carbon to yield an enolate anion. The LDA produces kinetic (less substituted) enolate anion. In Step 2, the newly formed enolate anion, which is nucleophilic at the $\text{α}$ carbon, attacks the molecule of the given aldehyde. The immediate product is an alkoxide anion (${\text{RO}}^{\text{-}}$), which is subsequently protonated in Step 3. The condensation occurs without heat owing to the extended conjugation with aromatic ring in an $\text{α,β -unsaturated}$ carbonyl compound. The dehydration of $\text{β -hydroxycarbonyl}$ compound takes place by a proton transfer followed by heterolysis step in which the ${\text{HO}}^{\text{-}}$ leaving group departs to yield the overall product.

The complete, detailed mechanism and the major organic product for the given reaction is as shown below:

Conclusion

The complete, detailed mechanism and the major organic product for given reaction is drawn by crossed aldol reaction followed by dehydration of $\text{β -hydroxycarbonyl}$ compound.

Interpretation Introduction

(b)

Interpretation:

The complete, detailed mechanism and the major organic product for given reaction is to be drawn.

Concept introduction:

When ketone is treated with sodium hydroxide, the product $\text{β -hydroxycarbonyl}$ compound is formed. The carbonyl and the hydroxyl groups in the product are separated by two carbon atoms. In Step 1, ${\text{HO}}^{\text{-}}$ deprotonates the $\text{α}$ carbon to yield an enolate anion. NaOH produces thermodynamic (more substituted) enolate anion. In Step 2, the newly formed enolate anion, which is nucleophilic at $\text{α}$ carbon, attacks another carbonyl carbon present in the molecule. This is called the crossed aldol reaction. The immediate product is an alkoxide anion (${\text{RO}}^{\text{-}}$), which is subsequently protonated in Step 3. The dehydration of $\text{β -hydroxycarbonyl}$ compound takes place. But if the $\text{α}$ carbon of $\text{β -hydroxycarbonyl}$ compound does not have the hydrogen atom the dehydration would not takes place.

Answer to Problem 18.68P

The complete, detailed mechanism and the major organic product for given reaction is as shown below:

Explanation of Solution

The given reaction is as shown below:

The given reaction is a crossed aldol reaction. In Step 1, ${\text{HO}}^{\text{-}}$ deprotonates the $\text{α}$ carbon of the ketone to yield an enolate anion. NaOH produces thermodynamic (more substituted) enolate anion. In Step 2, the newly formed enolate anion, which is nucleophilic at the $\text{α}$ carbon, attacks the molecule of the given aldehyde. The immediate product is an alkoxide anion (${\text{RO}}^{\text{-}}$), which is subsequently protonated in Step 3. As the $\text{α}$ carbon of $\text{β -hydroxycarbonyl}$ compound does not have any H atom, the aldol condensation mechanism does not take place. The complete, detailed mechanism and the major organic product for the given reaction is as shown below:

Conclusion

The complete, detailed mechanism and the major organic product for given reaction is drawn on the basis of crossed aldol reaction mechanism.

Interpretation Introduction

(c)

Interpretation:

The complete, detailed mechanism and the major organic product for given reaction is to be drawn.

Concept introduction:

When aldehyde is treated with sodium hydroxide, the product $\text{β -hydroxycarbonyl}$ compound (an aldol ) is formed. The carbonyl and the hydroxyl groups in the product are separated by two carbon atoms. In Step 1, ${\text{HO}}^{\text{-}}$ deprotonates the $\text{α}$ carbon to yield an enolate anion. In Step 2, the newly formed enolate anion, which is nucleophilic at the $\text{α}$ carbon, attacks second carbonyl carbon of the aldehyde. The immediate product is an alkoxide anion (${\text{RO}}^{\text{-}}$), which is subsequently protonated in Step 3. If the reaction is heated, then dehydration occurs and water is eliminated from the $\text{β -hydroxycarbonyl}$ compound, giving the overall product a $\text{C=C}$ double bond. This overall reaction, in which an aldol addition is followed by dehydration, is called an aldol condensation. The product of an aldol condensation is an $\text{α,β -unsaturated}$ carbonyl compound. Under basic conditions, dehydration of $\text{β -hydroxycarbonyl}$ compound takes place via an E1cb mechanism, which stands for elimination, unimolecular, conjugate base. Step 1 is a proton transfer, generating a resonance-stabilized enolate anion. In Step 2, the ${\text{HO}}^{\text{-}}$ leaving group departs to yield the overall product.

Answer to Problem 18.68P

The complete, detailed mechanism and the major organic product for given reaction is as shown below:

Explanation of Solution

The given reaction is

The given reaction is intramolecular aldol condensation reaction as the sodium hydroxide and heat is given. The given aldehyde is treated with sodium hydroxide, to produce $\text{β -hydroxycarbonyl}$ compound (an aldol ). In Step 1, ${\text{HO}}^{\text{-}}$ deprotonates the $\text{α}$ carbon of one carbonyl group which produces a five membered ring as a product. In Step 2, the newly formed enolate anion, which is nucleophilic at the $\text{α}$ carbon, attacks the carbon of second carbonyl group of the given aldehyde. The intramolecular addition takes place. The immediate product is an alkoxide anion (${\text{RO}}^{\text{-}}$), which is subsequently protonated in Step 3. As the reaction is heated, dehydration occurs and water is eliminated from the $\text{β -hydroxycarbonyl}$ compound, giving the overall product a $\text{C=C}$ double bond. The dehydration of $\text{β -hydroxycarbonyl}$ compound takes place via an E1cb mechanism. In this step 1 is a proton transfer, generating a resonance-stabilized enolate anion. In Step 2, the ${\text{HO}}^{\text{-}}$ leaving group departs to yield the overall product.

The complete, detailed mechanism and the major organic product for the given reaction is as shown below:

Conclusion

The complete, detailed mechanism and the major organic product for given reaction is drawn on the basis of intramolecular aldol condensation reaction.

Interpretation Introduction

(d)

Interpretation:

The complete, detailed mechanism and the major organic product for given reaction is to be drawn.

Concept introduction:

When ketone is treated with strong base like LDA, the product enolate anion is formed. In Step 1, LDA deprotonates the $\text{α}$ carbon of the carbonyl group to yield an enolate anion. The LDA produces kinetic (less substituted) enolate anion. In Step 2, the newly formed enolate anion, which is nucleophilic at the $\text{α}$ carbon, attacks the carbonyl group characteristics of the aldehyde over the one characteristic of a ketone. The immediate product is an alkoxide anion (${\text{RO}}^{\text{-}}$), which is subsequently protonated in Step 3. The condensation occurs without heat owing to the extended conjugation with aromatic ring in an $\text{α,β -unsaturated}$ carbonyl compound. The dehydration occurs and water is eliminated from the $\text{β -hydroxycarbonyl}$ compound, giving the overall product a $\text{C=C}$ double bond. The dehydration of $\text{β -hydroxycarbonyl}$ compound takes place by proton transfer step followed by heterolysis step and the ${\text{HO}}^{\text{-}}$ leaving group departs to yield the overall product.

Answer to Problem 18.68P

The complete, detailed mechanism and the major organic product for given reaction is as shown below,

Explanation of Solution

The given reaction is

Firstly, the given ketone is treated with LDA, to produce $\text{β -hydroxycarbonyl}$ compound (an aldol ). In Step 1, base LDA deprotonates the $\text{α}$ carbon of the carbonyl of ketone to yield an enolate anion. The LDA produces kinetic (less substituted) enolate anion. In Step 2, the newly formed enolate anion, which is nucleophilic at the $\text{α}$ carbon, attacks carbonyl carbon of the characteristics of aldehyde over a ketone group. The immediate product is an alkoxide anion (${\text{RO}}^{\text{-}}$), which is subsequently protonated in Step 3. The condensation occurs without heat owing to the extended conjugation with aromatic ring in an $\text{α,β -unsaturated}$ carbonyl compound. The dehydration of $\text{β -hydroxycarbonyl}$ compound takes place by a proton transfer, followed by heterolysis step in which the ${\text{HO}}^{\text{-}}$ leaving group departs to yield the overall product.

The complete, detailed mechanism and the major organic product for given reaction is as shown below,

Conclusion

The complete, detailed mechanism and the major organic product for given reaction is drawn by aldol addition reaction followed by dehydration of $\text{β -hydroxycarbonyl}$ compound.