Lecture 7: Aromatic Aldehydes & Ketones

Lecture 7: Aromatic Aldehydes & Ketones

• Aromatic aldehydes and ketones are a category of carbonyl compounds
• These compounds contain a carbonyl group (C=O)
• Examples of carbonyl compounds include aldehydes, ketones, carboxylic acids, esters, and amides
• Aliphatic aldehydes are named by replacing the "-e" of the corresponding alkane name with "-al"
• Aldehyde groups attached to ring systems are named by adding "-carbaldehyde" to the ring name
• Aliphatic ketones are named by replacing the "-e" of the corresponding alkane name with "-one"
• The carbon atom of the carbonyl group is numbered to give it the lowest possible number
• Ketones can also be named by naming the two groups attached to the carbonyl carbon and adding the word "ketone"

Intended Learning Outcomes (ILO's)

• Students will be able to identify structural differences between aldehydes and ketones
• Students will be able to name aldehydes and ketones using IUPAC nomenclature
• Students will be able to synthesize aldehydes and ketones
• Students will be able to explain nucleophilic reactions at the carbonyl carbon

Aromatic Aldehyde and Ketones - Page 15

• Aromatic aldehydes and ketones are a class of carbonyl compounds
• The carbonyl group (C=O) is a characteristic feature of these compounds

Nomenclature of Aldehydes and Ketones - Page 15

• Aliphatic aldehydes are named by replacing the final "-e" in the alkane name with "-al"
• Aldehydes attached to a ring system are named by adding "-carbaldehyde" to the ring name
• Aliphatic ketones are named by replacing the "-e" in the alkane name with "-one"
• The carbonyl carbon is numbered to provide the lowest possible number

Synthesis of Aldehydes and Ketones from Alcohols

• Primary alcohols can be oxidized to aldehydes
• Secondary alcohols can be oxidized to ketones

Reactions of Aldehydes and Ketones - Page 221

• The most important reaction of aldehydes and ketones are nucleophilic addition reactions
• A nucleophile (electron-rich species) reacts with the electron-deficient carbonyl carbon
• Nucleophilic addition involves three fundamental events:
  • Formation of a new C-Nu bond
  • Breaking of the C=O bond
  • Protonation of the alkoxide intermediate
• Nucleophilic addition is a key reaction for aldehydes and ketones

Example of Nucleophilic Addition Reaction (Addition of Hydrogen Cyanide (HCN)) - Page 238

• Great care must be taken when working with HCN due to its toxicity and volatility
• Reactions involving HCN should be conducted in a fume hood

Addition of Organometallic Compounds: Grignard Reagents (RMgX) - Page 240

• Grignard reagents react with formaldehyde to produce primary alcohols
• Grignard reagents react with other aldehydes to yield secondary alcohols
• Grignard reagents react with ketones to generate tertiary alcohols

Addition of Derivatives of Ammonia

• Aldehydes and ketones react with ammonia derivatives to form different compounds

Addition of Alcohols (Page 224)

• Aldehydes and ketones react with alcohols to form hemiacetals and acetals

Addition of Hydride Ion

• Reducing agents like NaBH4 convert ketones into alcohols

Addition of Carbanions: The Knoevenagel Condensation - Page 372

• The Knoevenagel reaction is a modified aldol reaction
• It involves the reaction of carbonyl compounds with active methylene compounds in the presence of weakly basic conditions
• It proceeds through an enolate intermediate

Addition of Ylides: The Wittig Reaction

• The Wittig reaction involves the reaction of aldehydes or ketones with phosphorous ylides
• This results in the formation of alkenes.

Oxidation Reactions

• Aldehydes are easily oxidized to carboxylic acids
• Ketones are more resistant to oxidation because they lack a readily oxidizable hydrogen atom

Haloform Reaction

• This reaction occurs with methyl ketones
• The methyl ketone is converted to a carboxylate ion, X, and a haloform (e.g., chloroform)
• This reaction is generally accompanied by the formation of a yellow precipitate (iodoform)

References, Textbooks, and Online Resources

• Several textbooks (Elements of organic chemistry by H. Zimmerman and I. Zimmerman, Solomons, T.W. Graham Organic Chemistry) and online references (chem.libretexts.org and khanacademy.org) are cited.

Class Activity-1

• Students are instructed to provide structural formulas for cyclohexanecarbaldehyde, 3-methylcyclohexanecarbaldehyde, and 2,2-dibromocyclopentanecarbaldehyde

Natural Compounds Containing Aldehyde and Ketones

• Examples of natural compounds that contain aldehydes and ketones, including cinnamaldehyde, vanillin, citral, and various hormones (testosterone, progesterone, cortisone) are highlighted in structural formulas and their source.