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Question:
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Which one of the following alkenes will react faster with $\mathrm{H}_2$ under catalytic hydrogenation conditions?
Options:
- A
- B
- C
- D
Solution:
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Verified Answer
The correct answer is:
Due to steric hinderence, hyperconjugation and heat of hydrogenation, reactivity of alkenes can be shown as:
$$
\begin{aligned}
& \mathrm{H}_2 \mathrm{C}=\mathrm{CH}_2>\mathrm{R}-\mathrm{CH}=\mathrm{CH}_2> \\
& \mathrm{R}-\mathrm{CH}=\mathrm{CH}-\mathrm{R}>\mathrm{R}_2 \mathrm{C}=\mathrm{CH}_2> \\
& \mathrm{R}_2 \mathrm{C}=\mathrm{CHR}>\mathrm{R}_2 \mathrm{C}=\mathrm{CR}_2 .
\end{aligned}
$$
Related Theory
The relative rates of hydrogenation decrease with the increase of steric hindrance. In order of stability of alkene, most stable the alkene slowly it gives the product.
$$
\begin{aligned}
& \mathrm{H}_2 \mathrm{C}=\mathrm{CH}_2>\mathrm{R}-\mathrm{CH}=\mathrm{CH}_2> \\
& \mathrm{R}-\mathrm{CH}=\mathrm{CH}-\mathrm{R}>\mathrm{R}_2 \mathrm{C}=\mathrm{CH}_2> \\
& \mathrm{R}_2 \mathrm{C}=\mathrm{CHR}>\mathrm{R}_2 \mathrm{C}=\mathrm{CR}_2 .
\end{aligned}
$$
Related Theory
The relative rates of hydrogenation decrease with the increase of steric hindrance. In order of stability of alkene, most stable the alkene slowly it gives the product.
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