CH+19+Worksheet 2

Nucleophilic Addition to Polar π Bonds

General Concepts

• Weak Nucleophiles: Under basic conditions, the nucleophile becomes stronger, facilitating reactions.

• Acid Catalysis: Under acidic conditions, the electrophile becomes stronger, enhancing reactivity.

Problem 19.1: Mechanisms

• Draw the mechanism for reactions under (a) basic conditions and (b) acidic conditions.

Reaction - HCN Addition

Details of Addition

• HCN addition is more complex compared to simple nucleophilic addition.

• Involves weak nucleophiles, making it unstable but can lead to significant products.

Product Prediction

Problem 19.2

• Predict the products resulting from various reactions.

Direct vs. Conjugate Addition

• Weak nucleophiles favor direct addition which can occur in neutral conditions.

Formation of Acetals, Imines, and Enamines

• Formation of acetals is favored in certain conditions.

• Reactants undergo 1,4-conjugate addition which is reversible and stabilizes through resonance.

Hydrolysis and Formation

Hydrolysis of Acetals

• Hydrolysis is a method for the formation of acetals.

• Formation of Imines and Enamines is tied to similar mechanisms as acetal formation.

Hydrolysis of Imines

• Process is akin to acetal formation but involves heterolysis to yield other products.

Hydrolysis of Enamines

Detailed Mechanism

• Hydrolysis leads to generation of starting materials. Understanding why certain reactions do not yield imines or enamines is critical.

Reduction Techniques

19.5 Reductive Amination

• Two steps: Initial formation of imine, followed by reduction to amine.

Example - Wolff-Kishner Reduction

• A reverse reaction leading to desired ketone/aldehyde products, requiring specific conditions without alpha hydrogens.

Predictive Tasks

Problem 19.15

• Predict products for specific reactions.

Aldol Addition

• Final Products Specification from retro-synthetic analysis.

Aldol Reactions

Key Concepts

• Discussed reactions involving ketones and crossed aldol reactions.

• Aldehyde addition to reactants to generate specific products.

Problem 19.8

• Use examples to predict product outcomes from described reactions.

Advanced Techniques

Generating Enolate Anions

• Mechanisms around enolate generation using strong bases (specifically LDA).

Robinson Annulation

• Utilize intramolecular reactions leveraging reactive conjugates for complex synthesis.

• Emphasize beta unsaturation for reactivity and product formation.

Additional Practice

Task Engagement

• Engage with mechanisms, synthesize amines from aldehydes/ketones.

• Explore synthesis routes through aldol addition/condensation.