ch-8 for summary

Unit Objectives

• Ability to write common and IUPAC names for aldehydes, ketones, and carboxylic acids.

• Draw structures for compounds with carbonyl and carboxyl functional groups.

• Understand preparation methods and reactions of these compounds.

• Correlate physical properties and chemical reactions of aldehydes, ketones, and carboxylic acids with their structures.

• Explain mechanisms for selected reactions of aldehydes and ketones.

• Understand factors influencing the acidity of carboxylic acids and their reactions.

• Know the uses of aldehydes, ketones, and carboxylic acids.

Importance of Carbonyl Compounds

• Carbonyl compounds comprise aldehydes, ketones, and carboxylic acids, which are crucial in organic chemistry.

• Found in various products: fabrics, flavourings, drugs, etc.

Concept Overview

Functional Groups

• Carbonyl Group (>C=O): Present in aldehydes (attached to carbon and hydrogen) and ketones (attached to two carbons).

• Carboxyl Group (-COOH): Formed by bonding the carbonyl carbon with hydroxyl (-OH).

• General Structures:

  • Aldehydes: RCHO

  • Ketones: RC(=O)R'

  • Carboxylic Acids: RCOOH

Key Definitions

• Aldehydes: Compounds with the carbonyl group bonded to at least one hydrogen.

• Ketones: Compounds where the carbonyl carbon is attached to two other carbons.

• Carboxylic Acids: Contain a carboxyl group.

• Amides: Contain nitrogen (-NH2) attached to carbonyl.

• Acyl Halides: Carbonyl carbon attached to halogens.

• Esters and Anhydrides: Derivatives of carboxylic acids.

Nomenclature of Aldehydes & Ketones

Common Names

• Derived from carboxylic acids, replacing the suffix -ic with -aldehyde.

• Examples:

  • Methanal (formaldehyde) from formic acid.

  • Ethanal (acetaldehyde) from acetic acid.

  • Common names may reflect source.

IUPAC Names

• Aldehydes: Replace -e with -al (e.g., hexanal).

• Ketones: Replace -e with -one (e.g., hexanone).

• Number longest chain from the carbonyl group, with substituents indicated.

Physical Properties of Aldehydes and Ketones

• Vary from gases to solids; lower members are highly volatile.

• Boiling points higher than ethers and hydrocarbons due to dipole-dipole interactions, but lower than alcohols (no H-bonding).

• Lower members miscible with water; solubility decreases with longer carbon chains.

• Odours range from pungent in small molecules to pleasant fragrances in larger ones (e.g., vanillin).

Chemical Reactions of Aldehydes and Ketones

Nucleophilic Addition Reactions

1. Mechanism:

   • Nucleophile attacks electrophilic carbon of carbonyl.

   • Formation of a tetrahedral intermediate.

   • Protonation leads to the neutral product.

2. Comparison of Reactivity:

   • Aldehydes generally more reactive than ketones due to steric hindrance and electronic factors.

Reactions

• HCN Addition: Forms cyanohydrin (useful intermediates).

• Sodium Hydrogensulfite Addition: Forms addition products, useful for purification.

• Grignard Reagents: React with aldehydes and ketones.

• Alcohol Addition: Forms hemiacetals and acetals.

• Reactions with ammonia derivatives: Forms imines and similar compounds.

Reduction Reactions

• Aldehydes and ketones can be reduced to alcohols; various reducing agents like NaBH4 and LiAlH4 used.

• Chemical tests differentiate between aldehydes and ketones (e.g., Tollens’ test, Fehling’s test).

Carboxylic Acids

General Properties

• Have the carboxyl (-COOH) functional group, stronger acids than phenols due to resonance stabilization of the conjugate base.

• Nomenclature uses the suffix -oic acid (alkane -> -oic acid).

Preparation methods

1. From Alcohols and Aldehydes: Easily oxidized with oxidizing agents like KMnO4 and K2Cr2O7.

2. From Nitriles: Hydrolysis leads to effective acid formation.

3. From Grignard Reagents: Reacting with carbon dioxide produces carboxylic acids.

Key Reactions

• Esterification: Forms esters with alcohols under acidic conditions.

• Decarboxylation: Loss of CO2 to form hydrocarbons, useful in synthetic organic chemistry.

• Halogenation: Involves a-hydrogens, leading to a-halocarboxylic acids (Hell-Volhard-Zelinsky reaction).

Uses of Aldehydes, Ketones, and Carboxylic Acids

• Formaldehyde: Used in preservation and synthesis of polymers.

• Acetaldehyde: Key in manufacturing acetic acid and various chemicals.

• Benzaldehyde: Important in perfumes and dyes.

• Solvents: Acetone, methyl-ethyl-ketone used across industries.