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.
What is the name of the compound (D) in the reaction sequence given in the passage?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Butane
The passage states that (C) on dehydration gives a mixture of but-1-ene and but-2-ene, and that both of them on reduction give the same compound (D).
Reduction of an alkene with hydrogen (for example over Ni or Pt) adds H2 across the C=C double bond and gives the alkane with the same carbon chain. The two butenes differ only in the position of the double bond on the same unbranched four-carbon chain, so both give the same alkane:
\( \displaystyle \ce{CH3CH2CH=CH2 + H2} \xrightarrow{\ce{Ni}} \ce{CH3CH2CH2CH3} \)
\( \displaystyle \ce{CH3CH=CHCH3 + H2} \xrightarrow{\ce{Ni}} \ce{CH3CH2CH2CH3} \)
So (D) is butane.
Why the other options are incorrect
Option (2) Pentane — Incorrect. It has 5 carbon atoms; adding hydrogen does not change the four-carbon chain of the butenes.
Option (3) Propene — Incorrect. It still has a C=C double bond and only 3 carbon atoms; reduction removes the double bond.
Option (4) But-1-yne — Incorrect. It has a triple bond; it would need removal of hydrogen from a butene, the opposite of reduction.