Q77 / 200 · NEET 2005 · Chemistry
Which one of the following alkenes will react faster with $\mathrm{H}_2$ under catalytic hydrogenation conditions?
- Correct answerA

- B

- C

- D

Solution
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.
Hence, the correct answer is option: 'A'.