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Pinacol Pinacolone Rearrangement Questions

Pinacol is a white solid organic diol compound. It consists of two hydroxy groups (-OH) on vicinal carbon atoms. In contrast, Pinacolone is a colourless liquid ketone with a molecular formula of C6H12O. It has a peppermint or camphor-like odour. The rearrangement of pinacol to pinacolone is called pinacol pinacolone rearrangement.

Definition: The pinacol pinacolone rearrangement is an approach to convert a 1,2-diol (pinacol) to a carbonyl compound (pinacolone) under acidic conditions. The name of the reaction derives from the rearrangement of pinacol to pinacolone.

Pinacol Pinacolone Rearrangement Chemistry Questions with Solutions

Q1. What is the name of the first molecular rearrangement identified by chemists?

  1. Beckmann rearrangement
  2. Curtius rearrangement
  3. Claisen rearrangement
  4. Pinacole pinacolone rearrangement

Answer: (d), Pinacol pinacolone rearrangement is the first molecular rearrangement identified by chemists.

Q2. What is a rearrangement reaction?

Answer: A rearrangement reaction is a comprehensive class of organic reactions where an organic substituent migrates from one atom to another in the same or different species, resulting in a structural isomer of the original molecule.

For example, alkene on heating with a strong acid yields isomeric alkene.

Q3. What is a pinacol?

Answer: Pinacol is a white solid organic diol compound. It consists of two hydroxy groups (-OH) on vicinal carbon atoms. The simplest member of this group is 2,3- dimethyl- 2,3- butanediol.

Structure of Pinacol: Pinacol Pinacolone Rearrangement 03Q4. How can you synthesise a pinacol?

Answer: Pinacol can be synthesised by a pinacol coupling reaction of acetone. Foremost we heat a ketone with the magnesium amalgam, which is then reduced with water.

Q5. Which intermediate carbocation is more stable in pinacol pinacolone rearrangement?

  1. 1o carbocation
  2. 2o carbocation
  3. 3o carbocation
  4. 4o carbocation

Answer: ©, 3o carbocation is more stable in pinacol pinacolone rearrangement.

Q6. What is a pinacolone?

Answer: Pinacolone is a colourless liquid ketone with a molecular formula of C6H12O. It has a peppermint or camphor-like odour.

Structure of pinacolone:

Pinacol Pinacolone Rearrangement 04Q7. What is the IUPAC name of the simplest pinacolone?

Answer: The IUPAC name of simplest pinacolone is 3,3-dimethyl-2-butanone.

Pinacol Pinacolone Rearrangement 04

Q8. What is pinacol pinacolone rearrangement?

Answer: The pinacol pinacolone rearrangement is an approach to convert a 1,2-diol to a carbonyl compound. It takes place under acidic conditions. The name of the reaction derives from the rearrangement of pinacol to pinacolone.

Q9. Who discovered the pinacol pinacolone rearrangement?

  1. Wilhelm Rudolph Fittig
  2. Louis Pasteur
  3. Alfred Nobel
  4. Marie Curie

Answer: (a), The pinacol pinacolone rearrangement was discovered by Wilhelm Rudolph Fittig.

Q10. What is the IUPAC name of the simplest pinacol?

Answer: The IUPAC name of the simplest pinacol is 2,3- dimethyl- 2,3- butanediol.

Pinacol Pinacolone Rearrangement 03

Q11. How can you synthesise a pinacolone?

Answer: When pinacol is treated with dilute or moderately concentrated sulphuric acid, a rearrangement reaction occurs, leading to the formation of ketone called pinacolone. The rearrangement is known as pinacol-pinacolone or pinacolic rearrangement.

Q12. What are the applications of pinacolone?

Answer: Pinacolone plays an essential role in pharmaceutical industries.

  • Pinacolone is useful in manufacturing pesticides, herbicides, fungicides and fertilisers.
  • Pinacolone is useful in manufacturing stiripentol drugs.
  • Pinacolone is useful in manufacturing cyanoguanidine drugs.
  • Pinacolone is useful in the retrosynthetic analysis of vibunazole.

Q13. Explain pinacol pinacolone rearrangement in detail.

Answer: Pinacol is a white solid organic diol compound. It consists of two hydroxy groups (-OH) on vicinal carbon atoms. In contrast, Pinacolone is a colourless liquid ketone with a molecular formula of C6H12O. It has a peppermint or camphor-like odour.

The pinacol pinacolone rearrangement is an approach to convert a 1,2-diol (pinacol) to a carbonyl compound (pinacolone). It takes place under acidic conditions. The name of the reaction derives from the rearrangement of pinacol to pinacolone.

The reaction proceeds via the formation of a positively charged intermediate, and then the methyl group migrates from one carbon centre to another leading to the formation of pinacolone.

Q14. What is migratory aptitude?

Answer: The ease with which any group undergoes nucleophilic 1,2 shift is known as its migratory aptitude. All the groups do not migrate with equal ease in 1,2 nucleophilic rearrangement.

Q15. What is the order of migratory aptitude of different groups?

Answer: The ease with which any group undergoes nucleophilic 1,2 shift is known as its migratory aptitude. All the groups do not migrate with equal ease in 1,2 nucleophilic rearrangement.

The migratory aptitude of the phenyl group is more than hydrogen, which is more than the alkyl group. However, we can not apply it to unsymmetrical pinacol substrates. The most stable cation controls the reaction pathway in an unsymmetrical pinacol.

Practise Questions on Pinacol Pinacolone Rearrangement

Q1. Explain the mechanism of pinacol pinacolone rearrangement?

Q2. Enlist the factors that affect the formation of pinacolone.

Q3. Explain pinacol-like rearrangement of the epoxide.

Q4. What is semi-pinacol rearrangement?

Q5. Predict the products of the pinacol rearrangement of 2,3- dipheny| – 2,3- butanediol and 3-phenyl -1.2- propanediol. Give the name of a simple chemical test that would show whether your prediction was correct or not.

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