Question:
Which of the following alkenes will react fastest with \( \mathrm{H_2} \) under catalytic hydrogenation conditions?
• [(1)]
\(\mathrm{RCH=CHR}\)
• [(2)]
\(\mathrm{RCH=CH_2}\)
• [(3)]
\(\mathrm{R_2C=CHR}\)
• [(4)]
\(\mathrm{R_2C=CR_2}\)
Which of the following alkenes will react fastest with \( \mathrm{H_2} \) under catalytic hydrogenation conditions?
• [(1)] \(\mathrm{RCH=CHR}\)
• [(2)] \(\mathrm{RCH=CH_2}\)
• [(3)] \(\mathrm{R_2C=CHR}\)
• [(4)] \(\mathrm{R_2C=CR_2}\)
• [(1)] \(\mathrm{RCH=CHR}\)
• [(2)] \(\mathrm{RCH=CH_2}\)
• [(3)] \(\mathrm{R_2C=CHR}\)
• [(4)] \(\mathrm{R_2C=CR_2}\)
Show Hint
More substituted alkenes tend to react faster with hydrogen under catalytic conditions due to increased electronic density.
Updated On: Apr 22, 2026
- A
- B
- C
- D
Show Solution
Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Analyze the structure of the alkenes.
The reactivity of alkenes towards hydrogenation is affected by the structure and substituents on the carbon-carbon double bond. Alkenes with more substituted carbons typically react faster because the electronic density on the double bond is higher, making it more susceptible to attack by the catalyst.
Step 2: Analyze the options.
- Option (1): This alkene has only simple hydrogens on both sides of the double bond and will react slower.
- Option (2): This alkene has more substituted groups, making it react faster with hydrogen.
- Option (3): This alkene has a different arrangement, and its reactivity is somewhat lower.
- Option (4): This alkene is similarly substituted as option (3) and will react slower.
Step 3: Conclusion.
The correct answer is (2), as this alkene is more substituted and will react faster under catalytic hydrogenation conditions.
The reactivity of alkenes towards hydrogenation is affected by the structure and substituents on the carbon-carbon double bond. Alkenes with more substituted carbons typically react faster because the electronic density on the double bond is higher, making it more susceptible to attack by the catalyst.
Step 2: Analyze the options.
- Option (1): This alkene has only simple hydrogens on both sides of the double bond and will react slower.
- Option (2): This alkene has more substituted groups, making it react faster with hydrogen.
- Option (3): This alkene has a different arrangement, and its reactivity is somewhat lower.
- Option (4): This alkene is similarly substituted as option (3) and will react slower.
Step 3: Conclusion.
The correct answer is (2), as this alkene is more substituted and will react faster under catalytic hydrogenation conditions.
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