Which of the following statements are correct ?

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The treatment of 3 – heptyne with ${KMnO}_{4}$ under neutral conditions at room temperature gives ${CH}_{3} {CH}_{2} {COOH and CH}_{3} {CH}_{2} {CH}_{2} COOH$

The treatment of 3 – heptyne with ${KMnO}_{4}$ under alkaline or acidic conditions at higher temperatures gives

${CH}_{3} {CH}_{2} {COCOCH}_{2} {CH}_{2} {CH}_{3}$

The addition of HBr to 1, 3 – pentadiene proceeds at a faster proceeds at a faster rate than that to 1,4 – pentadiene

The addition of HBr to butadiene at – 80°C to give 1, 2 – adduct is kinetically controlled while that at 40°C to give 1,4 – adduct is thermodynamically controlled.

answer is C.

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Detailed Solution

(A) With neutral conditions at room temperature, a diketone is formed via the hydroxylation reaction.

(B) Under neutral of alkaline conditions at higher temperature, the triple bond is cleaved to give carboxylic acids.

$C H_{3} C H_{2} C \equiv {(C H_{2})}_{2} C H_{3} \overset{[0]}{\to} C H_{3} C H_{2} C O O H + H O O C {(C H_{2})}_{2} C H_{3}$

$C H_{2} = C H - C H = C H - C H_{3} \overset{H^{+}}{\to} C H_{3} - {C H}_{a l l y l i c}^{+} - \underset{C a r b o c a t i o n}{C H} = C H - C H_{3}$

$C H_{2} = C H - C H_{2} - C H = C H_{2} \overset{H^{+}}{\to} C H_{3} - {C H}_{2 º}^{+} - \underset{C a r b o c a t i o n}{C H_{2}} - C H = C H_{2}$

Allylic carbocation is more stable due to resonance

Its formation requires lesser $Δ H$ as compared to 2º carbocation and hence is formed at a faster rate.

The conversion allylic carbocation involves a lower $Δ H$ as compared to carbocation At low temperature, 1, 2-adduct is formed due to the lower $Δ H$ . Thus, it formation is kinetically- controlled. As temperature is raised,1,2- adduct passed over to the allylic carbocation and then to thermodynamically more stable 1,4-adduct. The 1,4-adduct is more stable as it is a more substituted as the conversion of 1,4 adduct to intermediate complex involves a lerger $Δ H$ value

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