Organic Chemistry 2 - Lecture 6: Carbonyl Compounds

Introduction

• Final lecture of Organic Chemistry 2
• Focus on carbonyl compounds
• Overview of functional groups covered:
  • Alkanes, alkenes, alkynes
  • Alcohols, ethers, haloalkanes
  • Aromatic compounds, amines

Carbonyl Compounds Overview

• Structure: Carbon double bonded to oxygen (C=O)
• Common Examples: Aldehydes, ketones, carboxylic acids
• Reactions:
  • Nucleophilic substitution
  • Nucleophilic addition

Characteristics of Carbonyl Groups

• Electrophilic Carbon:
  • Oxygen more electronegative than carbon
  • Formation of a dipole (carbon is partial positive, oxygen is partial negative)
• Hybridization:
  • SP2 hybridized
  • Planar structure with 120-degree bond angles

Nucleophilic Substitution Reactions

• Occurs when carbonyl carbon has a good leaving group
• Good Leaving Groups: Halides, esters, amides
• Examples:
  • Acid halides, anhydrides, esters, amides
• Mechanism:
  • Nucleophile attacks carbonyl carbon
  • Electrons pushed to oxygen forming tetrahedral intermediate
  • Reformation of carbonyl and expulsion of leaving group

Leaving Group Characteristics

• Good Leaving Groups:
  • Electronegative
  • Stable when they leave
  • Weaker bases make better leaving groups
• Example Assessment:
  • Chloride (Cl-) as a good leaving group (pKa < 13)
  • Hydroxide (OH-) poor leaving group (pKa > 13)
  • Methoxide better than hydroxide

Nucleophilic Addition Reactions

• Occurs when no good leaving group is present
• Examples: Aldehydes, ketones
• Mechanism:
  • Nucleophile attacks carbonyl
  • Electrons pushed into oxygen
  • Forms tetrahedral intermediate without substitution
  • Requires acid work-up to protonate oxygen

Comparative Reactivity

• Aldehydes more reactive than ketones
• Ketones more reactive than carboxylic acid derivatives

Practical Applications

• Carbonyls in biological compounds (e.g., cortisone)
• Importance of understanding carbonyl reactions in organic synthesis

Conclusion

• Summary of topics covered in Organic Chemistry 2
• Encouragement to support the lecturer for teaching awards
• Look forward to future courses in Organic Chemistry

This lecture provides a comprehensive understanding of carbonyl compounds, their structures, reactions, and the importance of good leaving groups in reactions. Understanding these concepts is crucial for advanced studies and applications in organic chemistry.