Unit 18: Aldehydes and Ketones
The carbonyl as the course's key electrophile: a nucleophile drops in from above, and the tetrahedral intermediate it forms goes six different directions.
7 topics · 24 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Nomenclature and Relative Reactivity of Carbonyls
- How it worksHow does having one fewer bulky alkyl group and less electron donation leave an aldehyde's carbon more open to attack?
- Worked exampleFind the correct IUPAC name for CH3CH2COCH3.
- Going furtherWhat happens to a carbonyl's electrophilicity when an electron-withdrawing group like a halogen sits nearby on the chain?
Your turn1 of 2
What is the correct IUPAC name for CH3CH2COCH3?Nucleophilic Addition to the Carbonyl
- How it worksHow does a nucleophile's attack push a carbonyl's π electrons entirely onto the oxygen, forming a tetrahedral alkoxide?
- Worked exampleFind the product when cyanide adds to acetaldehyde to form a cyanohydrin.
- Common mistakeWhy doesn't nucleophilic addition to a carbonyl ever kick out a leaving group the way substitution at an alkyl halide does?
- Ties togetherHow does this tetrahedral-intermediate logic reappear, with a leaving group added back in, once you reach carboxylic acid derivatives?
Your turn1 of 2
Cyanide adds to acetaldehyde to form a cyanohydrin. What is the product?Hydration and Hemiacetal Formation
- How it worksHow does water add across a carbonyl to form a geminal diol, and how does an alcohol do the same to form a hemiacetal?
- Worked exampleFind the hemiacetal product formed when methanol adds to acetaldehyde under acid catalysis.
- Going furtherWhat happens to a sugar's own structure when one of its hydroxyl groups cyclizes to form an intramolecular hemiacetal?
Your turn1 of 2
Methanol adds to acetaldehyde under acid catalysis to form a hemiacetal. What is the product?Acetal Formation as a Protecting Group
- How it worksHow does a hemiacetal lose water and pick up a second alcohol under acid catalysis to become a full acetal?
- Worked exampleFind the acetal product when cyclohexanone reacts with excess ethylene glycol under acid catalysis.
- Ties togetherHow does protecting a ketone as an acetal let a Grignard reagent react safely with a different carbonyl on the same molecule?
Your turn1 of 2
Cyclohexanone reacts with excess ethylene glycol under acid catalysis. What is the acetal product?Imine and Enamine Formation
- How it worksHow does a primary amine lose water after addition to form an imine, while a secondary amine loses water differently to form an enamine?
- Worked exampleFind the imine product when cyclohexanone reacts with methylamine under mildly acidic conditions.
- Common mistakeWhy doesn't a tertiary amine react with a ketone the same way a primary or secondary amine does?
- Going furtherWhat happens to the product when a secondary amine, instead of a primary one, reacts with the same carbonyl?
Your turn1 of 2
Cyclohexanone reacts with methylamine under mildly acidic conditions. What is the imine product?The Wittig Reaction
- How it worksHow does a phosphorus ylide attack a carbonyl, forming a four-membered ring that collapses into a new π bond and a phosphine oxide?
- Worked exampleFind the alkene product when the ylide from bromomethyltriphenylphosphonium reacts with cyclohexanone.
- Common mistakeWhy doesn't the Wittig reaction ever leave an alcohol as its final product the way a Grignard addition does?
- Going furtherWhat happens to a synthesis plan once the Wittig reaction lets a chemist place a double bond exactly where a carbonyl used to sit?
Your turn1 of 2
The ylide generated from bromomethyltriphenylphosphonium reacts with cyclohexanone. What is the alkene product?Reduction of Aldehydes and Ketones
- How it worksHow does sodium borohydride deliver a hydride to the carbonyl carbon the same way a Grignard's carbanion would?
- Worked exampleFind the alcohol product when cyclohexanone is treated with sodium borohydride followed by an aqueous workup.
- Going furtherWhat happens to a molecule with both a ketone and an ester when it is treated with the stronger reducing agent lithium aluminum hydride?
Your turn1 of 2
Cyclohexanone is treated with sodium borohydride followed by an aqueous workup. What is the alcohol product?