Propose mechanisms for the following reactions.
(b)

Verified step by step guidance

1. Step 1: Recognize the reaction type. This is a condensation reaction between an aldehyde (acetaldehyde, CH₃CHO) and phenylhydrazine (PhNHNH₂) under acidic conditions. The product is a hydrazone derivative.
2. Step 2: Protonation of the carbonyl oxygen. In the presence of acid (H⁺), the oxygen atom of the aldehyde is protonated, increasing the electrophilicity of the carbonyl carbon.
3. Step 3: Nucleophilic attack by phenylhydrazine. The lone pair on the nitrogen of PhNHNH₂ attacks the carbonyl carbon, forming a tetrahedral intermediate.
4. Step 4: Elimination of water. After the intermediate forms, a proton transfer occurs, followed by the elimination of a water molecule to form a C=N double bond.
5. Step 5: Formation of the hydrazone. The final product is stabilized as the hydrazone derivative, where the phenyl group (Ph) is attached to the nitrogen atom of the C=N bond.

Key Concepts

Reaction Mechanisms

A reaction mechanism is a step-by-step description of how a chemical reaction occurs at the molecular level. It outlines the sequence of elementary steps, including bond breaking and formation, and the intermediates formed during the reaction. Understanding mechanisms is crucial for predicting the products and understanding the kinetics and thermodynamics of the reaction.

Types of Organic Reactions

Organic reactions can be classified into several types, including substitution, addition, elimination, and rearrangement reactions. Each type has distinct characteristics and mechanisms. Recognizing the type of reaction helps in predicting the behavior of reactants and the nature of the products formed, which is essential for proposing accurate mechanisms.

Curved Arrow Notation

Curved arrow notation is a visual representation used in organic chemistry to illustrate the movement of electrons during a reaction. Arrows indicate the direction of electron flow, showing how bonds are broken and formed. Mastery of this notation is vital for accurately depicting reaction mechanisms and understanding the underlying processes in organic reactions.