Write the mechanism for each of the following reactions:
b. the reaction of benzoyl chloride with excess methylamine to form N-methylbenzamide

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Identify the functional groups involved in the reaction. Benzoyl chloride contains an acyl chloride group (-COCl), which is highly reactive, and methylamine (CH₃NH₂) is a nucleophile due to the lone pair of electrons on the nitrogen atom.

Recognize the type of reaction. This is a nucleophilic acyl substitution reaction, where the nucleophile (methylamine) attacks the electrophilic carbonyl carbon of benzoyl chloride, leading to the substitution of the chloride group.

Step 1: The lone pair of electrons on the nitrogen atom of methylamine attacks the carbonyl carbon of benzoyl chloride. This forms a tetrahedral intermediate, where the carbonyl oxygen temporarily gains a negative charge.

Step 2: The tetrahedral intermediate collapses, reforming the carbonyl group. This results in the expulsion of the chloride ion (Cl⁻) as a leaving group, forming an amide bond between the benzoyl group and the methylamine.

Step 3: Since excess methylamine is present, it can act as a base to neutralize the H⁺ released during the reaction, forming N-methylbenzamide as the final product.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction in organic chemistry where a nucleophile attacks the electrophilic carbon of a carbonyl group, leading to the substitution of a leaving group. In the case of benzoyl chloride, the chlorine atom is the leaving group, and methylamine acts as the nucleophile. This mechanism is crucial for understanding how amides are formed from acyl chlorides.

Amine Reactivity

Amines are nucleophilic compounds that can react with electrophiles due to the presence of a lone pair of electrons on the nitrogen atom. In this reaction, excess methylamine not only attacks the carbonyl carbon of benzoyl chloride but can also lead to the formation of N-methylbenzamide. Understanding the reactivity of amines is essential for predicting the outcome of reactions involving these compounds.

Formation of Amides

Amides are organic compounds characterized by the presence of a carbonyl group (C=O) directly bonded to a nitrogen atom. The formation of amides from acyl chlorides, such as benzoyl chloride, involves the nucleophilic attack of an amine, resulting in the formation of a stable amide bond. This concept is vital for grasping the significance of amide formation in organic synthesis and its applications in pharmaceuticals.

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