Study Notes on Aldehydes, Ketones, and Carboxylic Acids

Objectives and Importance

  • Recognize and write common and IUPAC names of aldehydes, ketones, and carboxylic acids.

  • Understand structures of compounds with carbonyl and carboxyl groups.

  • Describe preparation methods and reactions of these compounds.

  • Correlate physical properties and chemical reactions with structures.

  • Explain mechanisms of selected reactions involving aldehydes and ketones.

  • Comprehend factors influencing carboxylic acid acidity and their reactions.

  • Enumerate uses of aldehydes, ketones, and carboxylic acids.

Nomenclature of Aldehydes and Ketones

  • Aldehydes and ketones follow two naming systems:

    • Common names: Derived from carboxylic acids by replacing "-ic" with "-aldehyde" for aldehydes and naming two alkyl groups for ketones.

    • IUPAC names: Aldehydes use "-al" and ketones use "-one" (e.g., Butanal, Pentan-2-one).

Structure of Carbonyl Group

  • Carbonyl carbon (C=O) is sp²-hybridized, with bond angles ~120°.

  • Characteristics:

    • Carbonyl is polarized (C is electrophilic, O is nucleophilic).

    • Carbonyl compounds exhibit dipole moments, affecting reactivity.

Preparation of Aldehydes and Ketones

  • Oxidation of Alcohols: Primary alcohols yield aldehydes, secondary alcohols yield ketones.

  • Ozonolysis of Alkenes: Produces aldehydes or ketones.

  • Hydration of Alkynes: Water addition leads to aldehydes or ketones.

  • Side Chain Oxidation: Toluene oxidized to corresponding aldehydes.

  • Acyl Chlorides: React with Grignard reagents to form ketones.

Chemical Reactions

  • Aldehydes and ketones mainly undergo nucleophilic addition reactions:

    • Mechanism: Nucleophile attacks the carbonyl carbon, forming tetrahedral intermediate.

    • Aldehydes are generally more reactive than ketones due to sterics and electronics.

Physical Properties

  • Lower aldehydes/ketones: Soluble in water, higher members less soluble.

  • Boiling points higher than hydrocarbons due to dipole-dipole interactions; lower than alcohols (no hydrogen bonding).

Reactions of Carboxylic Acids

  • Preparation: From alcohols, aldehydes, or oxidation of alkylbenzenes.

  • Acidity: Stronger than alcohols; affected by electron-withdrawing groups, which stabilize the conjugate base.

  • Reactions:

    • Esterification with alcohols.

    • Halogenation in presence of red phosphorus (Hell-Volhard-Zelinsky reaction).

Uses

  • Aldehydes and ketones: Solvents, flavorings (e.g., Vanillin), pharmaceuticals.

  • Carboxylic acids: Preservatives, industrial chemicals, food additives, etc.