Wittig reaction is an organic chemical reaction wherein an aldehyde or a ketone reacts with triphenyl phosphonium ylide to form an alkene. It is used to extend the carbon chain or synthesise alkenes.
| Definition: A chemical reaction of an aldehyde or a ketone with triphenyl phosphonium ylide to form an alkene is known as a Wittig reaction. |
Wittig Reaction Chemistry Questions with Solutions
Q1. Which of the following is used as a reagent in a Wittig reaction?
(a) Monophenyl phosphonium ylide
(b) Diphenyl phosphonium ylide
(c) Triphenyl phosphonium ylide
(d) None of the above
Answer: (c) Triphenyl phosphonium ylide
Q2. Lithium diisopropyl amide (LDA) employs ______ in the Wittig reaction.
(a) Alpha alkylation
(b) Beta alkylation
(c) Gamma alkylation
(d) None of the above
Answer: (a) Alpha alkylation
Q3. Lithium diisopropyl amide (LDA) is a/an _______.
(a) Oxidising agent
(b) Reducing agent
(c ) Amphoteric amide
(d) None of the above
Answer: (b) Reducing agent
Q4. THF is the abbreviation of _______.
(a) Tetrahydrofuran
(b) Trihydrofuran
(c ) Trihalo Fluoride
(d) None of the above
Answer: (a) Tetrahydrofuran.
Q5. What are the end products of the Wittig reaction?
(a) Alkane and triphenylphosphine oxide
(b) Alkene and triphenylphosphine oxide
(c ) Alkyne and triphenylphosphine oxide
(d) None of the above
Answer: (b) Alkene and triphenylphosphine oxide
Q6. What is a Wittig reaction?
Answer: A chemical reaction of an aldehyde or a ketone with triphenyl phosphonium ylide to form an alkene is known as a Wittig reaction.
Q7. Why is sodium hydroxide used in the Wittig reaction?
Answer: Sodium hydroxide is used in the second step of the Wittig reaction. It deprotonates the reactant and forms the ylide (Wittig reagent).
Q8. What is ylide?
Answer: Ylide is a neutral dipolar molecule comprising a negatively charged nucleophile attached to a positively charged heteroatom with a formal positive charge.
Q9. Is the first step of Wittig reaction SN2?
Answer: Yes, the first step of Wittig reaction is SN2.. Phosphorus substitutes the bromine with methyl bromide leading to a bimolecular nucleophilic substitution (SN2) reaction.
Q10. Name the functional groups transformed in the Wittig reaction.
Answer: Hydroxyl, alkoxy, aromatic, nitro and ester groups are transformed in the Wittig reaction.
Q11. What is the limiting reagent in the Wittig reaction?
Answer: Benzyl triphenyl phosphonium chloride acts as a limiting reagent in the Wittig reaction.
Q12. Which types of isomers are formed in a rearrangement reaction?
Answer: Structural isomers are formed in a rearrangement reaction as the bond connectivity changes, but the molecular formula remains the same.
Q13. Why do we prefer primary alkyl halide to synthesise a Wittig reagent?
Answer: A primary alkyl halide is preferred to synthesise a Wittig reagent as the quaternisation of triphenylphosphine with secondary halides is commonly inefficient.
Q14. Is ylide a strong base?
Answer: Yes, ylide is a strong base. It is protonated by water, alcohol, or any other acidic hydrogen.
Q15. What is the primary difference between betaine and a ylide?
Answer: Betaine is a revised amino acid possessing glycine with three methyl groups. In contrast, ylide is a neutral dipolar molecule comprising a negatively charged nucleophile attached to a positively charged heteroatom with a formal positive charge.
Practise Questions on Wittig Reaction
Q1. Explain the mechanism of the Wittig reaction.
Q2. What are the advantages of the Wittig reaction?
Q3. What are the disadvantages of the Wittig reaction?
Q4. How can we synthesise a Wittig reagent?
Q5. What is the primary difference between ylide and zwitterion?
Click the PDF to check the answers for Practice Questions.
Download PDF
