Aldehydes and Ketones – NEET Chemistry Class 12

Aldehydes and Ketones are carbonyl compounds containing the C=O functional group. This chapter is crucial for NEET as it involves nucleophilic addition reactions, oxidation, reduction, and qualitative analysis tests. Questions often test both conceptual clarity and mechanism understanding.

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Introduction to Aldehydes and Ketones

• Aldehydes (R–CHO): Carbonyl group attached to at least one hydrogen atom.

• Ketones (R–CO–R’): Carbonyl group attached to two carbon atoms.

• Importance: Carbonyl group is polar, making aldehydes more reactive than ketones in nucleophilic addition.

Nomenclature

• Aldehydes: Suffix –al (e.g., Ethanal), carbonyl carbon numbered as C1

• Ketones: Suffix –one (e.g., Propanone), carbonyl carbon indicated in chain (e.g., Butan-2-one)

• Common names are sometimes used in NEET (e.g., Acetaldehyde, Acetone)

Physical Properties

• Polar C=O bond → higher boiling point than hydrocarbons

• Lower molecular weight compounds are soluble in water due to hydrogen bonding with –OH donors

• Aldehydes generally have lower boiling points than alcohols of similar molecular mass

Chemical Properties

1. Nucleophilic Addition Reactions:

   • Addition of HCN, NH₂OH, H₂, alcohols (hemiacetal/acetal formation)

   • Mechanism involves nucleophile attacking electrophilic carbon of C=O

2. Oxidation Reactions:

   • Aldehydes → Carboxylic acids using Tollen’s reagent or Fehling’s solution

   • Ketones are generally resistant to mild oxidizing agents

3. Reduction Reactions:

   • Aldehydes/Ketones → Alcohols using LiAlH₄ or NaBH₄

4. Condensation Reactions:

   • Aldol condensation, Cannizzaro reaction, Reaction with hydrazine derivatives (e.g., 2,4-DNP)

Reactivity and Mechanisms

• Aldehydes are more reactive than ketones due to less steric hindrance and inductive effects.

• Nucleophilic addition is the characteristic reaction of carbonyl compounds.

• Mechanisms often involve electrophilic carbonyl carbon and nucleophilic attack.

Importance for NEET Preparation

• Questions often involve reaction products, qualitative tests, and mechanisms.

• Carbonyl chemistry is fundamental for understanding subsequent organic reactions in carbohydrates, amino acids, and vitamins.

• Oxidation and reduction reactions are frequently tested in NEET numerical or theoretical questions.

Previous Year NEET Questions – Insights

• Tollen’s and Fehling’s test for aldehyde identification

• Nucleophilic addition reactions and their products

• Aldol condensation and Cannizzaro reaction problems

• Reduction of aldehydes/ketones to alcohols

• Comparative reactivity of aldehydes and ketones

Study Tips for Students

1. Memorize Nomenclature Rules – IUPAC and common names

2. Practice Reaction Mechanisms – Nucleophilic addition, oxidation, reduction, condensation

3. Understand Physical Properties – Polarity, solubility, boiling points

4. Refer NCERT Examples – NEET questions are closely aligned

5. Solve Previous Year Questions – Reinforces mechanism understanding and predicts exam pattern

Conclusion

Mastering Aldehydes and Ketones is essential for NEET success. It allows students to predict reaction outcomes, solve mechanism-based questions, and answer application-oriented problems confidently. A strong understanding ensures high scoring potential in Class 12 organic chemistry.