Aldehydes, Ketones and Carboxylic Acids for NEET UG
The C=O group is the most important functional group in organic chemistry. Aldehydes, ketones and carboxylic acids react mainly by nucleophilic addition, and a handful of named reactions cover most NEET questions.
ChemistryClass 1273 MCQs3 lessons14 flashcards3 memory tricks
Practise Aldehydes, Ketones and Carboxylic Acids free
What you'll learn
- Nucleophilic addition and tests for aldehydes
Explain why the carbonyl carbon is attacked by nucleophiles and distinguish aldehydes from ketones. - Named reactions
Recall the reagents and products of the key named reactions of carbonyl compounds. - Acidity of carboxylic acids
Explain and compare the acid strength of carboxylic acids.
Memory tricks
Aldehydes with no α-hydrogen (HCHO, C₆H₅CHO) undergo Cannizzaro with concentrated alkali. Those with α-H undergo aldol condensation with dilute alkali.
Compounds with CH₃CO– or CH₃CH(OH)– give a yellow precipitate of CHI₃ with I₂ and NaOH.
Aldehydes reduce Tollens' reagent (silver mirror) and Fehling's solution (red Cu₂O). Ketones generally don't, though α-hydroxy ketones such as fructose do.
Try 3 NEET-style questions
Q1. Carboxylic acids have higher boiling points than alcohols of similar molar mass mainly because
- they are ionic compounds
- they have larger molecules
- they cannot form hydrogen bonds
- they form strongly hydrogen-bonded dimers
Show answer
Answer: (4) they form strongly hydrogen-bonded dimers
Two carboxylic acid molecules form a cyclic dimer held by two hydrogen bonds, which persists even in the vapour, raising the boiling point.
Q2. The strongest acid among the following is
- CH₃COOH
- ClCH₂COOH
- Cl₂CHCOOH
- CCl₃COOH
Show answer
Answer: (4) CCl₃COOH
More electron-withdrawing Cl atoms stabilise the carboxylate ion more: trichloroacetic acid is strongest.
Q3. Toluene is oxidised to benzaldehyde using chromyl chloride (CrO₂Cl₂) followed by hydrolysis. This is the
- Rosenmund reduction
- Gattermann–Koch reaction
- Etard reaction
- Cannizzaro reaction
Show answer
Answer: (3) Etard reaction
In the Etard reaction chromyl chloride oxidises the methyl group of toluene to a chromium complex, which hydrolyses to benzaldehyde.
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