Give plausible explanation for each of t | Class 12 Chemistry Chapter Aldehydes Ketones and Carboxylic Acids, Aldehydes Ketones and Carboxylic Acids NCERT Solutions

Welcome to the NCERT Solutions for Class 12 Chemistry - Chapter Aldehydes Ketones and Carboxylic Acids. This page offers a step-by-step solution to the specific question from Exercise 2, Question 18: . With detailed answers and explanations for each chapter, students can strengthen their understanding and prepare confidently for exams. Ideal for CBSE and other board students, this resource will simplify your study experience.

Question 18:

Give plausible explanation for each of the following:

(i) Cyclohexanone forms cyanohydrin in good yield but 2, 2, 6 trimethylcyclohexanone does not.

(ii) There are two -NH2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones.

(iii) During the preparation of esters from a carboxylic acid and an alcohol in the presence of an acid catalyst, the water or the ester should be removed as soon as it is formed.

Answer:

(i) Cyclohexanones form cyanohydrins according to the following equation.

In this case, the nucleophile CN - can easily attack without any steric hindrance. However, in the case of 2, 2, 6 trimethylcydohexanone, methyl groups at α-positions offer steric hindrances and as a result, CN - cannot attack effectively.

For this reason, it does not form a cyanohydrin.

 

(ii) Semicarbazide undergoes resonance involving only one of the two - NH2 groups, which is attached directly to the carbonyl-carbon atom.

Therefore, the electron density on - NH2 group involved in the resonance also decreases. As a result, it cannot act as a nucleophile. Since the other - NH2 group is not involved in resonance; it can act as a nucleophile and can attack carbonyl-carbon atoms of aldehydes and ketones to produce semicarbazones.

 

(iii) Ester along with water is formed reversibly from a carboxylic acid and an alcohol in presence of an acid.

If either water or ester is not removed as soon as it is formed, then it reacts to give back the reactants as the reaction is reversible. Therefore, to shift the equilibrium in the forward direction i.e., to produce more ester, either of the two should be removed.


Study Tips for Answering NCERT Questions:

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  • Read the question carefully and focus on the core concept being asked.
  • Reference examples and data from the chapter when answering questions about Aldehydes Ketones and Carboxylic Acids.
  • Review previous year question papers to get an idea of how such questions may be framed in exams.
  • Practice answering questions within the time limit to improve your speed and accuracy.
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Comments

  • Subhangini
  • Jul 27, 2019

Thank u so much for providing the answers


  • Ak
  • Mar 11, 2019

Thanks


  • None
  • Mar 10, 2019

Many conversions are wrong


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Welcome to the NCERT Solutions for Class 12 Chemistry - Chapter . This page offers a step-by-step solution to the specific question from Excercise 2 , Question 18: Give plausible explanation for each of the following: (i) Cyclohexanone forms cyanohydrin in good....