Question

Two isomers 'A' and 'B' with molecular formula C₄H₈ give different products on oxidation with KMnO₄ in acidic medium. Isomer 'A' on reaction with KMnO₄/H⁺ results in the effervescence of gas and gives ketone. The compound 'A' is:

Options

• But-1-ene

• cis-But-2-ene

• trans-But-2-ene

• 2-methyl propene

Answer 1

2-methyl propene

Explanation:

Two isomers with molecular formula C₄H₈ are:

\[\begin{array}{cc}
\ce{H3C}\phantom{........................................}\\
\backslash\phantom{....................................}\\
\ce{C = CH2 and CH3-CH2-CH = CH2}\\
/\phantom{....................................}\\
\ce{H3C}\phantom{.........................................}
\end{array}\]

(i) \[\begin{array}{cc}
\phantom{}\ce{H3C}\phantom{..............}\ce{H3C}\phantom{....................}\\
\phantom{}\backslash\phantom{.................}\backslash\phantom{...............}\\
\ce{C = CH2 ->[KMnO4][H^+] C = O + CO2}\\
\phantom{}/\phantom{................}/\phantom{...............}\\
\phantom{.}\ce{H3C}\phantom{.............}\ce{H3C}\phantom{.....................}\\
\end{array}\]

(ii) \[\ce{CH3-CH2-CH = CH2 ->[KMnO4][H^+] CH3-CH2COOH + CO2}\]

So, Isomer (A) is (H₃C)₂ C = CH₂ as it gives ketone and CO₂.