Many of the condensations we have studied are reversible. The reverse reactions are often given the prefix retro-, the Latin word meaning “backward.” Propose mechanisms to account for the following reactions.
(c)

Verified step by step guidance

1. Step 1: Recognize that this is a retro-Michael reaction, which involves the reverse of a Michael addition. The reaction occurs under basic conditions (presence of OH⁻) and breaks the bond formed during the original Michael addition.
2. Step 2: Identify the bond that will be broken. In this case, the bond between the β-carbon of the ketone and the α-carbon of the nitrile group will be cleaved.
3. Step 3: Under basic conditions, the hydroxide ion (OH⁻) abstracts a proton from the α-carbon of the nitrile group, forming a carbanion at this position.
4. Step 4: The carbanion then facilitates the cleavage of the bond between the β-carbon of the ketone and the α-carbon of the nitrile group, resulting in the formation of the ketone and the alkene (H₂C=CH-CN).
5. Step 5: Verify the products formed. The ketone remains intact, and the alkene (H₂C=CH-CN) is generated as a result of the bond cleavage. This completes the retro-Michael reaction mechanism.

Key Concepts

Condensation Reactions

Condensation reactions involve the combination of two molecules to form a larger molecule, typically with the loss of a small molecule such as water. These reactions are fundamental in organic chemistry, as they are key in forming complex structures like esters, amides, and polymers. Understanding the conditions and reagents that facilitate these reactions is crucial for predicting the products formed.

Retro Reactions

Retro reactions, or retro-condensation, refer to the reverse of a condensation reaction, where a larger molecule breaks down into smaller components, often releasing a small molecule like water. This concept is important for understanding the equilibrium between reactants and products in reversible reactions, and it helps in predicting the direction of the reaction under specific conditions.

Reaction Mechanisms

A reaction mechanism is a step-by-step description of the pathway taken during a chemical reaction, detailing the sequence of bond-breaking and bond-forming events. Understanding mechanisms is essential for predicting the products of a reaction, as well as for designing synthetic routes in organic chemistry. Mechanisms often involve intermediates and transition states that provide insight into the reactivity and stability of the involved species.