An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives a mixture of but-1-ene and but-2-ene, both of which on reduction give (D). (C) on oxidation with pyridinium chlorochromate (PCC) gives (E), which is an aldehyde.
Identify the compound (C) in the reaction sequence given in the passage.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Butan-1-ol
Reading the reaction sequence in the passage:
Compound (A) is an ester: C8H16O2 is hydrolysed by acid to a carboxylic acid (B) and an alcohol (C).
Compounds (B) and (C) have the same carbon chain: oxidation of (C) gives (B), and oxidation does not change the number of carbon atoms. So each has half of the 8 carbon atoms: 4 carbon atoms.
Compound (C) is a primary alcohol: only a primary alcohol is oxidised to a carboxylic acid with the same number of carbons, and its PCC oxidation gives an aldehyde (E).
The chain is unbranched: dehydration gives a mixture of but-1-ene, \( \ce{CH3CH2CH=CH2} \), and but-2-ene, \( \ce{CH3CH=CHCH3} \); both are unbranched alkenes.
So (C) is \( \ce{CH3CH2CH2CH2OH} \), butan-1-ol. On heating with concentrated sulphuric acid it loses water; but-2-ene forms by rearrangement to a secondary carbocation:
\( \displaystyle \ce{CH3CH2CH2CH2OH} \xrightarrow[\Delta]{\text{conc. }\ce{H2SO4}} \ce{CH3CH2CH=CH2 + H2O} \)
\( \displaystyle \ce{CH3CH2CH2CH2OH} \xrightarrow[\Delta]{\text{conc. }\ce{H2SO4}} \ce{CH3CH=CHCH3 + H2O} \)
Why the other options are incorrect
Option (2) Butan-2-ol — Incorrect. It is a secondary alcohol; oxidation gives a ketone (butan-2-one), not a carboxylic acid or an aldehyde.
Option (3) Propan-1-ol — Incorrect. It has only 3 carbon atoms; it cannot give butenes, and its ester with propanoic acid would be C6H12O2.
Option (4) Pentan-2-ol — Incorrect. It has 5 carbon atoms and is a secondary alcohol, which gives a ketone on oxidation.
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “… A better reagent for oxidation of primary alcohols to aldehydes in good yield is pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HCl.”