Chapter 17, Problem 17.47P

Interpretation Introduction

(a)

Interpretation:

The mechanism for the given reaction is to be drawn, and the major product is to be predicted.

Concept introduction:

Organometallic compounds have a polar covalent $\text{C-M}$ bond. For example, the Grignard reagent ($\text{RMgX}$) has a polar $\text{C-Mg}$ bond, and an alkyl lithium reagent ($\text{RLi}$) has a polar covalent $\text{C-Li}$ bond. Since carbon is bonded with an electropositive element, it possesses a partial negative charge and acts as the nucleophile as well as the base and can be treated as ${\text{C}}^{\text{-}}$ donor. Thus, it is used to form a new $\text{C-C}$ bond with an electrophilic carbon. The nucleophilic part (${\text{R}}^{\text{-}}$) of the organometallic reagent shows a nucleophilic addition reaction with carbonyl compounds. In case of an aldehyde, on treatment with the organometallic reagent such as Grignard reagent ($\text{RMgX}$) or an alkyl lithium reagent ($\text{RLi}$) followed by the acidic workup, the corresponding secondary alcohol is formed, while ketones give tertiary alcohol as the product.

Answer to Problem 17.47P

The mechanism for the given reaction is drawn below:

The major product of the given reaction is

Explanation of Solution

The given reaction is

In the given reaction, the starting material is a cyclic ketone, and the organometallic reagent is Grignard reagent ($\text{PhMgBr}$). So the first step is the nucleophilic attack of the ${\text{Ph}}^{\text{-}}$ ion at the electrophilic carbon of the given starting material, which generates an alkoxide ion.

An alkoxide ion, on acid workup, forms uncharged alcohol as the final product.

Thus, the major product of the given reaction is

Conclusion

Ketones, when treated with Grignard reagent, produce tertiary alcohol as the final product.

Interpretation Introduction

(b)

Interpretation:

The mechanism for the given reaction is to be drawn, and the major product is to be predicted.

Concept introduction:

Organometallic compounds have a polar covalent $\text{C-M}$ bond. For example, the Grignard reagent ($\text{RMgX}$) has a polar $\text{C-Mg}$ bond, and an alkyl lithium reagent ($\text{RLi}$) has a polar covalent $\text{C-Li}$ bond. Since carbon is bonded with an electropositive element, it possesses a partial negative charge and acts as the nucleophile as well as the base and can be treated as ${\text{C}}^{\text{-}}$ donor. Thus, it is used to form a new $\text{C-C}$ bond with an electrophilic carbon. The nucleophilic part (${\text{R}}^{\text{-}}$) of the organometallic reagent shows a nucleophilic addition reaction with carbonyl compounds. In case of an aldehyde, on treatment with the organometallic reagent such as Grignard reagent ($\text{RMgX}$) or an alkyl lithium reagent ($\text{RLi}$) followed by the acidic workup, the corresponding secondary alcohol is formed, while ketones give tertiary alcohol as the product.

Answer to Problem 17.47P

The mechanism for the given reaction is drawn below:

The major product of the given reaction is

Explanation of Solution

The given reaction is

In the given reaction, the starting material is an aldehyde and the organometallic reagent is butyl lithium ($\text{nBuLi}$). So the first step is the nucleophilic attack of the butyl ion at the carbonyl carbon atom of the aldehyde to generate an alkoxide ion.

An alkoxide ion, on acid workup, forms uncharged alcohol as the final product.

Thus, the major product of the given reaction is

Conclusion

Ketones, when treated with Grignard reagent, produce tertiary alcohol as the final product.

Interpretation Introduction

(c)

Interpretation:

The mechanism for the given reaction is to be drawn, and the major product for the same reaction is to be predicted.

Concept introduction:

Although ${\text{CO}}_2$ is a non-polar compound, each $\text{C=O}$ bond is highly polar, and the central carbon atom in the ${\text{CO}}_2$ molecule is quite electron-poor. Thus, it is susceptible to a nucleophilic attack. Grignard reagents can add to ${\text{CO}}_2$ the reaction known as carboxylation reaction. The immediate product of carboxylation is a carboxylate ion, which is subsequently protonated through an acid workup to yield a carboxylic acid.

Answer to Problem 17.47P

The mechanism for the given reaction is drawn below:

The major product of the given reaction is

Explanation of Solution

The given reaction is

Each $\text{C=O}$ bond is highly polar, and the central carbon atom in the ${\text{CO}}_2$ molecule is quite electron-poor. Thus, it is susceptible to a nucleophilic attack. Grignard reagents can add to ${\text{CO}}_2$ the reaction known as carboxylation reaction.

The first step of the reaction is the attack of the nucleophile ${\text{CH}}_{\text{3}}{}^{\text{-}}$ on the carbon atom in ${\text{CO}}_2$ molecule. This will generate the carboxylate ion as shown below:

The immediate product of carboxylation is a carboxylate ion, which is subsequently protonated through an acid workup to yield a carboxylic acid.

Thus, the major product of the given reaction is

Conclusion

The Grignard reagent adds across the ${\text{CO}}_2$ molecule to yield a carboxylic acid as the final product.