Organic Chemistry Chapter 8: Aldehydes & Ketones

Chapter 8: Aldehydes and Ketones

• Aldehydes (RCHO) and ketones (R₂CO) are characterized by the carbonyl functional group (C=O).
• These compounds are widely found in nature as intermediates in metabolism and biosynthesis.
• Examples include pyridoxal phosphate (PLP) and hydrocortisone.

Functional Group Priority

• A list of functional groups, ranked from highest to lowest priority, for determining the parent chain in naming organic compounds.
  • Carboxylic acids
  • Esters
  • Amides
  • Nitriles
  • Aldehydes
  • Ketones
  • Alcohols
  • Amines
  • Alkenes/Alkynes
  • Alkanes
  • Ethers
  • Halides

Naming Aldehydes

• Aldehydes are named by replacing the terminal -e of the corresponding alkane name with -al.
• The parent chain must contain the -CHO group.
• If the -CHO group is attached to a ring, use the suffix carbaldehyde.
• Examples of common aldehydes and their systematic names are provided in a table.

Naming Ketones

• Replace the terminal -e of the alkane name with -one.
• The parent chain is the longest chain containing the ketone group.
• Numbering begins at the end nearer the carbonyl carbon.
• Some ketones have common names, like acetone.

Preparing Aldehydes and Ketones

• Primary alcohols can be oxidized to aldehydes using PCC in dichloromethane.
• Alkenes can be oxidized to aldehydes and ketones using ozone.
• Esters can be reduced to aldehydes using diisobutylaluminum hydride (DIBAL-H).
• A 2º alcohol can be oxidized to a Ketone

Preparing Ketones

• A 2º alcohol can be oxidized to a ketone.
• Ozonolysis of alkenes can yield ketones if one of the unsaturated carbon atoms is disubstituted.

Oxidation of Aldehydes and Ketones

• Aldehydes are oxidized efficiently to carboxylic acids by CrO3 in aqueous acid.
• Ketones are oxidized with difficulty using hot, alkaline KMnO4, resulting in the cleavage of the C-C bond next to the carbonyl group to form carboxylic acids. Reaction is practical for symmetrical ketones.

Nucleophilic Addition of H₂O (Hydration)

• Aldehydes and ketones react with water to form 1,1-diols (geminal diols).
• This reaction is reversible, meaning a gem diol can eliminate water.

Addition of H-Y to C=O

• Formation of the product is often readily reversible (unstable alcohol).
• Favored when Y is an electronegative element that substitutes with the carbonyl group, such as halogen's.

Nucleophilic Addition of HCN (Cyanohydrin Formation)

• Aldehydes and unhindered ketones react with HCN to yield cyanohydrins.
• The addition of HCN is reversible and base-catalyzed.
• Addition of CN- to C=O yields a tetrahedral intermediate, which gets protonated.

Nucleophilic Addition of Grignard Reagents and Hydride Reagents

• Treatment of aldehydes or ketones with Grignard reagents yields an alcohol.
• Treatment of aldehydes or ketones with hydride reagents (LiAlH4 and NaBH4) yields an alcohol through reduction reaction.

Keto-Enol Tautomerism

• A carbonyl compound with a hydrogen atom on its alpha carbon rapidly equilibrates with its corresponding enol.
• Compounds that differ only by the position of a moveable proton are called tautomers.

Enols

• The enol tautomer is usually present to a very small extent and can not be isolated.
• Since the enol tautomer rapidly forms, it serves as a reaction intermediate.

β-Dicarbonyls

• When a hydrogen atom is flanked by two carbonyl groups, its acidity is enhanced.
• The negative charge of the enolate delocalizes over both carbonyl groups, increasing its stability.

Carbonyl Condensation: The Aldol Reaction

• Aldehydes and ketones react with another molecule, forming a β-hydroxy carbonyl compound.
• This product (the aldol) dehydrates to yield conjugated enones in acidic or basic conditions.

Practical Mixed Aldols

• Reactions using carbonyl partners without α-hydrogens are more likely to be successful and yield mixed aldol products.

Mixed Aldols with Acidic Carbonyl Compounds

• Ethyl acetoacetate forms its enolate ion under less basic conditions.
• Aldol condensation reactions involving ethyl acetoacetate generally favor a mixed product.

The Claisen Condensation Reaction

• Reacting an ester with one equivalent of a base yields a β-keto ester.

Explore the intriguing world of aldehydes and ketones in this quiz based on Chapter 8 of Organic Chemistry. Understand their structures, naming conventions, and functional group priorities, as well as their significance in nature and organic synthesis. Test your knowledge on these crucial carbonyl compounds!