Chemistry Hydrocarbons MDCAT 2019
PMDC Verified Question 34 of 65
Alkenes undergo:
A
Nucleophilic substitution
B
Nucleophilic addition
C
Electrophilic substitution
D
Electrophilic Addition
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Electrophilic Addition
Concept:

The characteristic reaction of a functional group is dictated by its electronic nature. Alkenes contain an electron-rich, easily accessible pi bond.

Solution:

  • Because the pi bond (\( \text{C}=\text{C} \)) has loosely held electrons situated above and below the molecular plane, it acts as a strong nucleophile.


  • It instinctively attacks electron-deficient species (electrophiles).


  • The pi bond breaks entirely, allowing new atoms to add to the carbon skeleton without any atoms leaving, thereby restoring stable single bonds.


  • Consequently, the primary, characteristic reaction mechanism for alkenes is Electrophilic Addition.


Why other options are incorrect:

  • Nucleophiles are repelled by the high electron density of the pi bond, making nucleophilic attacks rare.


  • Substitution implies removing an atom, which is less energetically favorable than simply adding across the easily broken pi bond. (Electrophilic substitution is typical for stable aromatic rings).

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