Solved Practice Questions on LiAlH4, NaBh4 & grignard reagent | Organic Chemistry PDF Download

Q.1. Which of the following reactions gives a product different from that of the other reactions?
(a)
(b)
(c)
(d)

Correct Answer is Option (c)

Reaction (c) gives a tertiary alcohol, 3-ethylpentan-3-ol, by reaction of two equivalents of the Grignard reagent with the ester, while the other reactions give the same secondary alcohol, pentan-3-ol.

Q.2. Which of the following reactions does not give a primary alcohol?
(a)
(b)
(c)
(d)

Correct Answer is Option (b)

In reaction (b), the ester cannot be reduced with NaBH₄.

Q.3. Which pair of reactants for a Grignard reaction does not give triphenylmethanol after an aqueous workup?

(a)

(b)

(c)

(d)

Correct Answer is Option (a)

In reaction (a), the aldehyde reacts with just one equivalent of the Grignard reagent, and the main product will be diphenylmethanol.

Q.4. Which is the reduction product of A/-methylpropanamide with LiAIH₄ in ether followed by an aqueous workup?
(a)
(b) CH₃CH₂CH₂NHCH₃ 
(c) CH₃CH₂CH₂OH
(d) CH₃CH₂CH₂NH₂

Correct Answer is Option (b)

LiAIH₄ is a powerful hydride donor which generally reduces all types of carbonyl functional groups, and its reduction of an amide gives an amine.

Q.5. Which is the reduction product of ethyl 3-oxobutanoate with NaBH₄ in methanol?
(a)
(b)
(c)
(d)

Correct Answer is Option (c)

NaBH₄ is a mild hydride donor which, in general, reduces aldehydes and ketones but not esters.

Q.6. Which of the following reactions does not give the product indicated?
(a)
(b)
(c)
(d)

Correct Answer is Option (d)

Grignard reagents are strong bases as well as nucleophiles, so reaction (d) gives cyclohexane as the result of proton transfer from H₂O.

Q.7. Which of the following reactions does not give a secondary alcohol?
(a)
(b)
(c)
(d)

Correct Answer is Option (d)

In reaction (d), the ester reacts with two equivalents of the Grignard reagent to give a tertiary alcohol after an aqueous workup.

Q.8. Which pair of reactants for a Grignard reaction does not give 2-phenylbutan-2-ol after an aqueous workup?
(a)
(b)
(c)
(d)

Correct Answer is Option (d)

In reaction (d), the product of the reaction of the ester and two equivalents of the Grignard reagent is 2-phenylpropan-2-ol.

Q.9. Which is the main reduction product of ethyl 3-oxobutanoate with LiAIH₄ in ether followed by an aqueous workup?
(a)
(b)
(c)
(d)

Correct Answer is Option (a)

LiAIH₄ is a powerful hydride donor which generally reduces all types of carbonyl functional groups. 

Q.10. Which is unreactive in hydride reduction with NaBH₄?
(a)
(b)
(c)
(d)

Correct Answer is Option (c)
NaBH₄ is a mild hydride donor which, in general, reduces aldehydes and ketones but not esters.