Introduction to Carbonyls and Class I Carbonyl Chemistry

Overview

• Carbonyls: Functional groups characterized by a carbon-oxygen double bond.
• Classes of Carbonyls:
  • Class 1: Includes esters, carboxylic acids, amides, anhydrides, and acid chlorides.
  • Class 2: Includes aldehydes and ketones.
  • Class 3: Focuses on alpha carbons and alpha hydrogens.

Class I Carbonyls

• Characteristics:
  • Have good leaving groups (e.g., anhydrides, esters, carboxylic acids, amides, acid chlorides).
  • Reaction involves nucleophile attacking the carbonyl, leading to a tetrahedral intermediate.
• Examples:
  • Anhydrides: Nucleophile attacks, oxygen leaves due to resonance stabilization.
  • Acid chlorides: Chlorine is a superb leaving group.

Class II Carbonyls

• Characteristics:
  • Aldehydes and ketones do not have good leaving groups.
  • Nucleophile attacks but no group is kicked out; forming carbanion is unfavorable.

Class III Carbonyls

• Focus:
  • On alpha carbon and alpha hydrogens.
  • Alpha hydrogens are acidic; a base can form an enolate ion.
  • Unique due to resonance stabilization with carbon-oxygen double bond.

Class I Carbonyl Chemistry

Basic Reaction

• Mechanism:
  • Nucleophile attacks carbonyl carbon.
  • Formation of a tetrahedral transition state.
  • Equilibrium process to determine which species is more reactive.

Acid Chlorides

• Reactions with:
  • Water/OH⁻: Form carboxylic acids.
  • Alcohols: Form esters.
  • Amines: Form amides.
  • Carboxylic acids: Form anhydrides.

Carboxylic Acids

• Reactions with:
  • Alcohols (under acidic conditions): Form esters.
  • Carboxylic acids (under acidic conditions): Form anhydrides.
  • Cannot directly form amides due to basic nature of nitrogen.

Amides

• Characteristics:
  • Exist predominantly in a stable form.
  • Require heat to activate (e.g., in biological processes like fevers).
• Reactions with:
  • Water (under acidic conditions and heat): Form carboxylic acids.
  • Alcohol (under acidic conditions and heat): Form esters.

Esters

• Reactions with:
  • Water (under acidic conditions): Form carboxylic acids.
  • Cannot directly form amides.

Anhydrides

• Reactions:
  • Can perform similar chemistry as acid chlorides due to good leaving group.

Forming Acid Chlorides

• Method:
  • Reaction of carboxylic acids with thionyl chloride.

Reactivity Order of Class I Carbonyls

• Acid chlorides > Anhydrides > Carboxylic acids = Esters > Amides

Conclusion

• Consistent mechanisms across Class I carbonyls.
• Importance of leaving group ability in determining reactivity.
• Recommendations: Review the video, practice mechanisms, engage in discussions for clarification.