Aldol Condensation and Cannizzaro Reaction - UNSOLVED PRACTICE SET

Q7. Write the mechanism for the aldol condensation of acetaldehyde. What is the final product after dehydration?

Q8. What is the Cannizzaro reaction? Write the reaction of benzaldehyde with concentrated NaOH.

Q9. Why does formaldehyde undergo Cannizzaro reaction but not aldol condensation?

Q10. Write the crossed aldol condensation between benzaldehyde and acetone. What is the major product?

Q11. What is the difference between aldol addition and aldol condensation? Give one example of each.

Q12. Your teacher shows you that benzaldehyde gives a Cannizzaro reaction with 50% NaOH. Write the reaction and identify the two products.

Q13. (a) Describe the mechanism of aldol condensation with a suitable example.

(b) What is the difference between aldol addition and aldol condensation?

(c) Explain why ketones undergo aldol condensation less readily than aldehydes.

(d) Write the mechanism of dehydration of aldol to α,β-unsaturated carbonyl compound.

Q14. (a) Describe the Cannizzaro reaction.

(b) Write the mechanism of Cannizzaro reaction using benzaldehyde as an example.

(c) Why do aldehydes without α-hydrogen undergo Cannizzaro reaction?

(d) What is crossed Cannizzaro reaction? Give an example.

Q15. (a) Explain the following:

(i) Intramolecular aldol condensation

(ii) Claisen-Schmidt condensation

Write examples for each.

(b) A compound with molecular formula C₈H₈O gives a positive Tollens' test and undergoes Cannizzaro reaction. Identify the compound and write the reaction.

Q16. A student studies the aldol condensation of acetaldehyde.

(a) Write the reaction for the self-condensation of acetaldehyde. What is the product called?

(b) If 44 g of acetaldehyde (molar mass = 44 g/mol) undergoes aldol condensation, calculate the theoretical yield of the aldol product (3-hydroxybutanal, molar mass = 88 g/mol).

(c) On heating, the aldol product dehydrates to give crotonaldehyde. Write the reaction and calculate the theoretical yield of crotonaldehyde (C₄H₆O, molar mass = 70 g/mol) from 44 g of acetaldehyde.

(d) In practice, the student obtains 35 g of crotonaldehyde. Calculate the percentage yield.

(e) Why is the yield less than 100%? (Consider at least two reasons.)

Q17. The following reactions involve aldol condensation and Cannizzaro reaction:

Reaction 1: 2CH₃CHO → CH₃CH(OH)CH₂CHO (dilute NaOH)

Reaction 2: 2HCHO + conc. NaOH → CH₃OH + HCOONa

Reaction 3: C₆H₅CHO + CH₃CHO → C₆H₅CH=CHCHO (dilute NaOH)

Reaction 4: 2C₆H₅CHO + conc. NaOH → C₆H₅CH₂OH + C₆H₅COONa

(a) Identify the type of reaction for each.

(b) For Reaction 1, explain why dilute NaOH is used instead of concentrated NaOH.

(c) For Reaction 2, calculate the mass of methanol obtained from 60 g of formaldehyde if the yield is 85%.

(d) For Reaction 3, why is benzaldehyde mixed with acetone in some crossed aldol condensations? What is the advantage?

(e) For Reaction 4, why does benzaldehyde not undergo aldol condensation? What structural feature determines this?

Q18. In a school chemistry lab, students perform aldol condensation and Cannizzaro reactions.

(a) A student mixes acetaldehyde with dilute NaOH. A viscous liquid forms. Write the reaction. Why does the product have a higher boiling point than acetaldehyde? (Consider hydrogen bonding.)

(b) Another student heats the product from (a) with dilute acid. A pungent-smelling liquid forms. Identify it and write the reaction.

(c) A third student performs the Cannizzaro reaction with formaldehyde. The products are methanol and sodium formate. Write the reaction. Why is formaldehyde particularly reactive in the Cannizzaro reaction?

(d) The students learn that in nature, aldol condensation is used to build complex molecules like sugars. How many aldol condensations are involved in the synthesis of glucose from simpler precursors? (General concept only.)

(e) The teacher asks: "If you were designing a synthesis route to produce a perfume ingredient (cinnamaldehyde), which reaction would you use and why?" Give your answer with reasoning.