Diborane reduces a. ester group b. nitro group c. halo group d. acid group

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Q. Diborane reduces a. ester group b. nitro group c. halo group d. acid group

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Step 1. Recall section 12.9.7's own statement. 'Carboxylic acid can also be reduced by diborane (diborane does not reduce -COOR, -NO2, -X).'

Step 2. Read the options against this. (a) ester group (-COOR) -- explicitly NOT reduced.

(b) nitro group (-NO2) -- explicitly NOT reduced.

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

MHT-CET 2026Set pcm-2026-04-19-M1 markMCQ
$_4$
›Reveal solutionSolution

LiAlH $_4$ is a powerful reducing agent that reduces $-$ COOH straight to $-$ CH $_2$ OH; the H $_3$ O $^+$ work-up then liberates the primary alcohol. Answer: option (A).

Carboxylic acids are difficult to reduce because the carbonyl carbon is stabilised by the adjacent $-$ OH. A strong nucleophilic hydride source is needed:

$R\text{-COOH} \xrightarrow{\text{(i) LiAlH}_4}\ \xrightarrow{\text{(ii) H}_3\text{O}^+} R\text{-CH}_2\text{OH}$ …
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MHT-CET 2020Set pcb-2020-10-01-PC1 markMCQ
$Q. Which of the following functional groups is reduced by diborane? (A) Nitro group (B) Halo group (C) Ester group (D) Carboxyl group$
›Reveal solutionSolution
Diborane selectively reduces carboxylic acids (–COOH → –CH₂OH) even in the presence of nitro, halo, or ester groups, which it does not readily attack.

Step 1 — Diborane's known chemoselectivity

Diborane (B₂H₆), typically used as a THF·BH₃ solution, is valued in synthesis precisely because it discriminates between functional groups. It reduces the carbonyl carbon of a carboxylic acid rapidly via hydroboration of the C=O, ultimately giving the primary alcohol after hydrolysis:
$R\text{–COOH} \xrightarrow{B_2H_6} R\text{–CH}_2OH$
Step 2 — Groups it does NOT touch under these mild conditions

Nitro group (–NO₂): unaffected

Halo group (C–X): unaffected …
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Q.Diborane reduces
a. ester group
b. nitro group
c. halo group
d. acid group

Concept understanding — Decarboxylation and Reduction of Carboxylic Acids

Q.Diborane reduces a. ester group b. nitro group c. halo group d. acid group

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Q.Diborane reduces
a. ester group
b. nitro group
c. halo group
d. acid group

Unlock everything free for 14 days