Nucleophilic Addition Reactions - UNSOLVED PRACTICE SET

Q7. Write the mechanism for the nucleophilic addition of HCN to acetaldehyde. Why is the reaction catalyzed by base?

Q8. What is the bisulphite addition reaction? Which aldehydes and ketones give this reaction?

Q9. Write the reaction of acetaldehyde with ethyl alcohol in presence of dry HCl. What is the product called?

Q10. What is the difference between a hemiacetal and an acetal? Give one example of each.

Q11. Write the reaction of acetone with hydroxylamine (NH₂OH). What is the product called?

Q12. Your teacher shows you that acetone gives a crystalline precipitate with 2,4-dinitrophenylhydrazine (2,4-DNP). What is the colour of this precipitate? Write the reaction.

Q13. (a) Describe the mechanism of nucleophilic addition to carbonyl compounds.

(b) Why do aldehydes undergo nucleophilic addition more readily than ketones?

(c) Explain the role of acid and base catalysis in nucleophilic addition reactions.

(d) Write the reactions of acetaldehyde with:

(i) HCN

(ii) NaHSO₃

(iii) CH₃OH (dry HCl)

(iv) NH₂OH

Q14. (a) Describe the addition of Grignard reagents to aldehydes and ketones.

(b) Write the reactions of CH₃MgBr with:

(i) HCHO

(ii) CH₃CHO

(iii) CH₃COCH₃

(iv) C₆H₅CHO

(c) What type of alcohol is formed in each case?

(d) Why must Grignard reactions be carried out in anhydrous conditions?

Q15. (a) Describe the reactions of aldehydes and ketones with ammonia derivatives:

(i) Hydroxylamine (NH₂OH)

(ii) Hydrazine (NH₂NH₂)

(iii) Phenylhydrazine (C₆H₅NHNH₂)

(iv) 2,4-Dinitrophenylhydrazine

Write the reactions and name the products.

(b) What is the significance of these reactions in qualitative analysis?

Q16. A student studies the addition of HCN to different carbonyl compounds.

(a) Write the reaction of HCN with acetaldehyde. What is the product called?

(b) Write the reaction of HCN with acetone. What is the product called?

(c) If 22 g of acetaldehyde (molar mass = 44 g/mol) reacts with excess HCN, calculate the theoretical yield of the cyanohydrin (molar mass = 85 g/mol).

(d) The addition of HCN to acetone is slower than to acetaldehyde. Explain why.

(e) A student claims that the cyanohydrin formed from benzaldehyde is optically active. Is this correct? Explain.

Q17. The following reactions involve nucleophilic addition to carbonyl compounds:

Reaction 1: CH₃CHO + NaHSO₃ → Product A

Reaction 2: CH₃COCH₃ + NH₂OH → Product B

Reaction 3: C₆H₅CHO + CH₃MgBr → Product C (after hydrolysis)

Reaction 4: CH₃CHO + 2CH₃OH → Product D (dry HCl)

(a) Identify products A, B, C, and D.

(b) For Reaction 1, why does acetone also give the reaction, but benzophenone does not?

(c) For Reaction 2, calculate the mass of product B obtained from 29 g of acetone if the yield is 80%.

(d) For Reaction 3, if 0.5 mol of CH₃MgBr is used with excess benzaldehyde, calculate the mass of product C obtained.

(e) For Reaction 4, why is dry HCl used? What would happen if water were present?

Q18. In a school chemistry lab, students perform various nucleophilic addition reactions.

(a) A student adds NaHSO₃ solution to acetaldehyde. A white crystalline precipitate forms. Write the reaction. Why does this precipitate dissolve on adding dilute acid or base?

(b) Another student prepares an oxime from cyclohexanone and hydroxylamine. Write the reaction. Why are oximes used in qualitative analysis?

(c) A third student performs the iodoform test on ethanol. A yellow precipitate forms. Write the reactions involved. Why is this test specific for compounds containing CH₃CO– or CH₃CH(OH)– groups?

(d) The students learn that semicarbazones are used to identify carbonyl compounds. Write the reaction of acetone with semicarbazide. Why is this derivative particularly useful?

(e) The teacher asks: "If you were designing a drug that needs to form a stable complex with a carbonyl compound in the body, which nucleophile (HCN, NH₂OH, or NH₂NH₂) would you choose and why?" Give your answer with reasoning.