Hsslive-xii-ch-anil-8. Aldehydes, Ketones and Carboxylic acids

Aldehydes, Ketones, and Carboxylic Acids

Overview

  • Compounds with carbon-oxygen double bonds

    • Carbonyl group: >C=O

  • Aldehydes: Carbonyl group is bonded to carbon and hydrogen.

  • Ketones: Carbonyl group is bonded to two carbon atoms.

  • Carboxylic acids: Carbonyl bonded to hydroxyl group (–OH).

  • Derivatives: Esters, anhydrides, amides, acyl halides.

Nomenclature

  • Aldehydes: Derived from corresponding carboxylic acid names by replacing "-ic acid" with "aldehyde".

  • Greek letters (α, β, γ, δ) are used for substituent position.

  • Ketones: Named from two alkyl or aryl groups, using suffix "-one". Positions indicated by Greek letters.

  • IUPAC names: Aldehydes (–al) and Ketones (–one) based on corresponding alkanes.

Examples

Aldehydes

Compound

Common Name

IUPAC Name

HCHO

Formaldehyde

Methanal

CH3CHO

Acetaldehyde

Ethanal

(CH3)2CHCHO

Isobutyraldehyde

2-Methylpropanal

CH3CH2CH2CH2CHO

Valeraldehyde

Pentanal

Ketones

Compound

Common Name

IUPAC Name

CH3-CO-CH3

Acetone

Propanone

CH3-CO-CH2-CH3

Ethyl methyl ketone

Butanone

CH3-CO-CH2-CH2-CH3

Methyl n-propyl ketone

Pentan-2-one

Preparation of Aldehydes and Ketones

  1. Oxidation of Alcohols:

    • Primary alcohols to aldehydes;

    • Secondary alcohols to ketones.

  2. Dehydrogenation of Alcohols:

    • Alcohols with copper/silver catalyst yield carbonyl compounds.

  3. Ozonolysis of Alkenes:

    • Using ozone followed by hydrolysis to form aldehydes or ketones.

  4. Hydration of Alkynes:

    • Alkyne plus water forms aldehydes/ketones.

  5. From Acyl Chlorides:

    • Rosenmund’s reduction gives aldehydes.

  6. From Nitriles & Esters:

    • Stephen reaction for aldehydes.

Physical Properties of Aldehydes and Ketones

  1. Boiling Point: Higher than hydrocarbons/ethers, lower than alcohols due to absence of hydrogen bonding.

  2. Solubility: Lower members miscible with water; solubility decreases with larger alkyl chains.

  3. State: Methanal (gas); ethanal/aceton volatile liquids; others may be liquids or solids.

Structure of the Carbonyl Group

  • Hybridization: sp2; forms 3 sigma bonds, 1 pi bond with oxygen.

  • Bond angles approx. 120 degrees; carbonyl carbon is electrophilic, oxygen nucleophilic.

Chemical Reactions of Aldehydes and Ketones

  1. Nucleophilic Addition Reactions: More reactive than ketones due to steric/electronic factors.

    • Addition of HCN, Grignard reagents, alcohols, ammonia, etc.

    • Formation of cyanohydrins, acetals, imines, oximes.

  2. Reduction: Converts aldehydes to primary alcohols; ketones to secondary alcohols.

  3. Oxidation: Aldehydes oxidized to carboxylic acids; ketones less easily oxidized.

  4. Haloform Reaction: Produces haloforms from aldehydes/ketones with methyl groups.

  5. Aldol Condensation: Forms β-hydroxy aldehydes/ketones; can undergo dehydration to yield α,β-unsaturated carbonyl compounds.

Carboxylic Acids

  • Definition: Compounds with carboxyl group (–COOH).

  • Nomenclature: Ends in –ic acid; derived from alkane names.

  • Preparation Methods:

  1. Oxidation of primary alcohols/aldehydes.

  2. Oxidation of alkylbenzenes.

  3. Hydrolysis of nitriles and Grignard reagents.

  4. Hydrolysis of acyl halides and anhydrides.

  5. Hydrolysis of esters.

Physical Properties and Reactions of Carboxylic Acids

  1. State: Colorless liquids (C<9) or waxy solids (C>9).

  2. Boiling Point: Higher than other organic compounds due to hydrogen bonding.

  3. Solubility: Soluble in water for lower acids; decreases with carbon length.

  4. Reactions: Acidity, esterification, oxidation, reduction, decarboxylation, and halogenation.

  5. Electrophilic Substitution: Deactivating, leads to meta derivatives.