Preparation of Ketones for NEET: Key Points, Tricks & MCQs
Preparation of KetonesAldehydes Ketones and Carboxylic AcidsNEET ChemistryNEET 2025Oxidation of AlcoholsOzonolysis
Preparation of Ketones for NEET: Key Points, Tricks & MCQs
Aldehydes, Ketones and Carboxylic Acids·2 min read·NEET 2026
What NEET Asks
Questions frequently test identifying reagents for oxidation of secondary alcohols and predicting products of reductive ozonolysis of alkenes.
Expect mechanism-based questions (qualitative understanding) and multi-step reactions involving these preparations.
Often seen in combination with other functional group conversions, contributing to 3-4 marks annually.
Key Points
Oxidation of Secondary Alcohols: Secondary (2°) alcohols (R-CH(OH)-R') are oxidized to ketones (R-CO-R').
Oxidizing Agents: Common reagents include PCC (Pyridinium Chlorochromate), CrO3/H2SO4 (Jones Reagent), K2Cr2O7/H+, KMnO4.
Mild Oxidation: PCC is often preferred for converting primary alcohols to aldehydes without over-oxidation, but for secondary alcohols, stronger agents also yield ketones reliably.
Ozonolysis of Alkenes: Alkenes (C=C) react with ozone (O3) followed by reductive work-up (e.g., Zn/H2O or (CH3)2S) to form carbonyl compounds.
Ketone Formation via Ozonolysis: For ketone formation, the alkene must have at least one carbon atom of the double bond substituted with two alkyl/aryl groups (R2C=CR'R'' → R2C=O + R'R''C=O or R2C=CR'2 → R2C=O + R'2C=O).
R₂C=CR'₂ + O₃ (1. O₃; 2. Zn/H₂O or (CH₃)₂S) → R₂C=O + R'₂C=O
```
* The double bond cleaves, and oxygen atoms attach to the fragmented carbons.
Common Mistakes
Students often confuse the products of oxidative ozonolysis (carboxylic acids for terminal aldehydes) with reductive ozonolysis (aldehydes/ketones).
Don't forget the second step (reductive work-up with Zn/H2O or Me2S) in ozonolysis; it's crucial to prevent H2O2 from further oxidizing aldehydes.
Students sometimes misidentify the starting alkene from the given ketone products of ozonolysis, especially with unsymmetrical alkenes.
Rapid Revision
Quickly recall: Secondary alcohols give ketones upon oxidation with various reagents. Reductive ozonolysis of alkenes substituted with alkyl/aryl groups at the double bond's carbons yields ketones. The double bond 'breaks' into two carbonyl groups.
Frequently Asked Questions
Which reagents are commonly used to oxidize secondary alcohols to ketones?▾
Common reagents for oxidizing secondary alcohols to ketones include chromium-based reagents like chromic acid (CrO3/H2SO4, Jones reagent), potassium dichromate (K2Cr2O7/H+), potassium permanganate (KMnO4), and milder options like PCC (Pyridinium Chlorochromate). All these efficiently convert 2° alcohols to ketones.
How does ozonolysis specifically lead to the formation of ketones?▾
Ozonolysis of an alkene yields ketones when the double-bonded carbon atoms are substituted with two alkyl or aryl groups. The alkene is first treated with ozone to form an ozonide, which is then cleaved reductively using reagents like Zn/H2O or (CH3)2S. This process breaks the C=C bond and inserts oxygen atoms, forming carbonyl compounds, including ketones if the substitution pattern is appropriate.
What is the key difference between oxidative and reductive ozonolysis concerning ketone formation?▾
For ketone formation, both oxidative and reductive ozonolysis produce ketones, as ketones are relatively stable to further oxidation. However, the distinction is crucial when aldehydes are formed. Reductive ozonolysis (with Zn/H2O or Me2S) stops at the aldehyde/ketone stage. Oxidative ozonolysis (without a reducing agent or with H2O2 workup) will oxidize any initially formed aldehydes to carboxylic acids, while ketones remain unaffected.
Practice MCQs on this topic
Interactive questions with instant AI explanations