Class 12 Chemistry - ISC
Aldehydes, Ketones and Carboxylic Acids
This Class 12 ISC Chemistry chapter explores carbonyl compounds—aldehydes, ketones, and carboxylic acids—which contain the carbon-oxygen double bond. You will study their methods of preparation, physical properties, and distinctive chemical reactions like nucleophilic addition, oxidation, and reduction. Carboxylic acid derivatives and acidity trends are heavily tested. Mastering name reactions such as Aldol condensation, Cannizzaro, and Rosenmund reduction is crucial for scoring high marks in your ISC board examinations.
Start Learning FreeKey Concepts
Nucleophilic Addition Reactions
Aldehydes and ketones readily undergo nucleophilic addition at the carbonyl carbon due to its electrophilic nature, with aldehydes being more reactive than ketones.
Aldol Condensation
Aldehydes and ketones having at least one alpha-hydrogen atom undergo self-condensation in the presence of a dilute base to form beta-hydroxy aldehydes or ketones.
Cannizzaro Reaction
Aldehydes lacking an alpha-hydrogen atom undergo self-oxidation and reduction (disproportionation) when treated with concentrated alkali to yield an alcohol and a salt of carboxylic acid.
Acidity of Carboxylic Acids
Carboxylic acids are acidic due to the resonance stabilization of their carboxylate anion, and electron-withdrawing groups increase their acidity while electron-donating groups decrease it.
Tollens' and Fehling's Tests
Distinctive laboratory tests used to differentiate between aldehydes (which give positive tests by reducing silver or copper ions) and ketones.
Important Formulas
Board Exam Info
In the ISC Class 12 Chemistry paper, this chapter typically carries around 6 to 8 marks. Questions frequently appear as name reactions, conversion series (A to B to C), distinguishing tests, and reasoning questions based on acidic strength or boiling points.
Frequently Asked Questions
Why are aldehydes generally more reactive than ketones towards nucleophilic addition?
Aldehydes are less sterically hindered and have fewer electron-donating alkyl groups than ketones, making the carbonyl carbon more electrophilic.
How can you distinguish between propan-2-one and propan-1-ol?
Propan-2-one (a ketone) will give a positive Iodoform test with iodine and sodium hydroxide, whereas propan-1-ol will not.
Why are carboxylic acids stronger acids than phenols?
The carboxylate anion formed after the loss of a proton in carboxylic acids is resonance-stabilized by two equivalent canonical structures, whereas the phenoxide ion has non-equivalent structures.
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