Introduction to Aldehydes and Ketones

  • Aldehydes and ketones are important classes of organic compounds.
  • They are widely used in various industries and play vital roles in biological processes.
  • In this lecture, we will focus on the IUPAC nomenclature for aldehydes and ketones.

Aldehydes: Definition and Examples

  • Aldehydes are organic compounds with a carbonyl group (-C=O) bonded to at least one hydrogen atom.
  • The general formula for aldehydes is R-CHO, where R represents an alkyl or aryl group.
  • Examples of aldehydes include formaldehyde (HCHO), acetaldehyde (CH3CHO), and benzaldehyde (C6H5CHO).

Ketones: Definition and Examples

  • Ketones are organic compounds with a carbonyl group (-C=O) bonded to two carbon atoms.
  • The general formula for ketones is R-CO-R’, where R and R’ represent alkyl or aryl groups.
  • Examples of ketones include acetone (CH3COCH3), propanone (CH3COCH2CH3), and benzophenone (C6H5COCH3).

IUPAC Nomenclature: Rules for Aldehydes

  1. Identify the longest carbon chain containing the aldehyde group.
  1. Number the carbon chain in a way that gives the aldehyde group the lowest possible number.
  1. Replace the “-e” ending of the corresponding alkane with “-al.”

Examples: IUPAC Nomenclature of Aldehydes

  • CH3CH2CHO: Butanal
  • CH3CHO: Ethanal (or acetaldehyde)
  • C6H5CHO: Benzaldehyde

IUPAC Nomenclature: Rules for Ketones

  1. Identify the longest carbon chain containing the ketone group.
  1. Number the carbon chain in a way that gives the ketone group the lowest possible number.
  1. Replace the “-e” ending of the corresponding alkane with “-one.”

Examples: IUPAC Nomenclature of Ketones

  • CH3COCH3: Propanone (or acetone)
  • CH3COCH2CH3: 2-Butanone (or ethyl methyl ketone)
  • C6H5COCH3: Benzophenone

Common Names for Aldehydes and Ketones

  • In addition to the IUPAC nomenclature, aldehydes and ketones also have common names.
  • For aldehydes, common names are derived from the names of corresponding carboxylic acids.
  • For ketones, common names are derived by adding the prefix “oxo-” before the parent alkane name.

Examples: Common Names of Aldehydes

  • CH3CH2CHO: Butyraldehyde
  • CH3CHO: Acetaldehyde
  • C6H5CHO: Benzaldehyde

Examples: Common Names of Ketones

  • CH3COCH3: Acetone
  • CH3COCH2CH3: Ethyl methyl ketone
  • C6H5COCH3: Phenyl methyl ketone ``markdown

Problem Solving Session Aldehydes And Ketones - IUPAC Nomenclature

  • Let’s solve some problems related to the IUPAC nomenclature of aldehydes and ketones.

Problem 1

Name the following compound: CH3CH2CHO

  • Solution: The longest carbon chain contains three carbon atoms with the aldehyde group attached. Thus, the compound is named as butanal.

Problem 2

Name the following compound: CH3COCH2CH3

  • Solution: The longest carbon chain contains four carbon atoms with the ketone group attached to the second carbon. Thus, the compound is named as 2-butanone (or ethyl methyl ketone).

Problem 3

Name the following compound: C6H5COCH3

  • Solution: The longest carbon chain contains seven carbon atoms with the ketone group attached to the second carbon. Thus, the compound is named as phenyl methyl ketone.

Problem 4

Give the IUPAC name for the following compound: HCHO

  • Solution: Since formaldehyde is the simplest aldehyde, it is also known as methanal.

Problem 5

Give the IUPAC name for the following compound: CH3COCH3

  • Solution: Acetone is the common and IUPAC name for this compound.

Problem 6

Give the IUPAC name for the following compound: CH3CHO

  • Solution: Acetaldehyde is the common and IUPAC name for this compound.

Problem 7

Convert the following common names into IUPAC names: a) Benzaldehyde b) Acetone c) Ethyl methyl ketone

  • Solution: a) C6H5CHO b) CH3COCH3 c) CH3COCH2CH3

Problem 8

Convert the following IUPAC names into common names: a) Butanal b) Propanone c) 2-Butanone

  • Solution: a) CH3CH2CHO b) CH3COCH3 c) CH3COCH2CH3

Summary

  • In this lecture, we covered the IUPAC nomenclature of aldehydes and ketones.
  • We learned the rules for naming aldehydes and ketones and saw examples of their IUPAC and common names.
  • Problem-solving exercises were provided to reinforce the concepts learned. ``

Physical Properties of Aldehydes and Ketones

  • Aldehydes and ketones are generally liquids or solids at room temperature.
  • The presence of the polar carbonyl group allows for hydrogen bonding between molecules, leading to higher boiling points compared to hydrocarbons.
  • Aldehydes and ketones have distinct odors, with some commonly used as fragrances or flavorings.

Chemical Reactions of Aldehydes

  • Aldehydes can undergo oxidation reactions to form carboxylic acids.
  • They can be reduced to primary alcohols using reducing agents like NaBH4 or LiAlH4.
  • Aldehydes can undergo nucleophilic addition reactions to form geminal diols.

Chemical Reactions of Ketones

  • Ketones are less reactive compared to aldehydes due to steric hindrance.
  • They can be reduced to secondary alcohols using reducing agents like NaBH4 or LiAlH4.
  • Ketones can undergo nucleophilic addition reactions to form hydrates.

Keto-Enol Tautomerism

  • Ketones and some aldehydes can exist in equilibrium with their corresponding enol forms.
  • Enols are tautomers of ketones and aldehydes, where the carbonyl oxygen is replaced by a hydroxyl group on the adjacent carbon.
  • This equilibrium occurs due to the movement of alpha hydrogen between carbon and oxygen atoms.

Aldol Condensation

  • Aldol condensation is a reaction between two molecules of aldehyde or one molecule of aldehyde and one molecule of ketone.
  • It involves the formation of a new carbon-carbon bond and leads to the formation of a β-hydroxyaldehyde or β-hydroxyketone.
  • The reaction proceeds through a nucleophilic addition followed by the elimination of water.

Cannizzaro Reaction

  • Cannizzaro reaction is a disproportionation reaction that occurs with certain aldehydes.
  • It involves the oxidation of one molecule of aldehyde to a carboxylic acid and the reduction of another molecule to an alcohol.
  • The reaction is facilitated by strong bases, such as concentrated alkali hydroxides.

Nucleophilic Addition of Cyanide

  • Aldehydes and ketones can undergo nucleophilic addition reactions with cyanide ion (CN-) to form cyanohydrins.
  • This reaction is an important step in the synthesis of various organic compounds, such as α-hydroxy acids.

Reduction of Aldehydes and Ketones

  • Aldehydes and ketones can be reduced to their respective alcohols using reducing agents like sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4).
  • The carbonyl group is reduced to a hydroxyl group, resulting in the formation of primary or secondary alcohols, depending on the starting compound.

Nucleophilic Addition of Grignard Reagents

  • Aldehydes and ketones react with Grignard reagents (RMgX) to form alcohols.
  • This reaction involves the nucleophilic addition of the carbon atom of the Grignard reagent to the carbonyl carbon, followed by protonation.

Summary

  • Aldehydes and ketones have distinct physical properties and can undergo various chemical reactions.
  • They can be oxidized or reduced to form different functional groups.
  • Keto-enol tautomerism, aldol condensation, Cannizzaro reaction, nucleophilic addition of cyanide, and reduction reactions are important reactions involving aldehydes and ketones.
  • Nucleophilic addition of Grignard reagents is another significant reaction.