Chemistry Hydrocarbons DUHS 2024
PMDC Verified Question 6 of 65
When an unsymmetrical alkene undergoes addition reactions, the negative part of attacking reagent is added to that double-bonded carbon atom which contains:
A
Highest number of chloride atoms
B
Lesser number of hydrogen atoms
C
Highest number of hydrogen atoms
D
Moderate number of hydrogen atoms
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Lesser number of hydrogen atoms
Concept:

This question asks for the formal definition of Markovnikov's Rule for the electrophilic addition to unsymmetrical alkenes.

Solution:

  • Markovnikov's rule states that when an unsymmetrical reagent (like HX) adds to an unsymmetrical alkene, the positive part (\( \text{H}^+ \)) goes to the carbon with the greater number of hydrogen atoms.


  • This ensures the formation of the most stable intermediate carbocation on the more highly substituted carbon.


  • Consequently, the negative part of the reagent (e.g., \( \text{X}^- \)) must attach to the carbocation, which is the carbon atom containing the lesser number of hydrogen atoms.


  • (Note: The source key erroneously selected C; however, B is the correct application of Markovnikov's Rule).


Why other options are incorrect:

  • Adding the negative part to the carbon with the highest number of hydrogen atoms (Option C) represents anti-Markovnikov addition, which only occurs under specific free-radical conditions (like HBr with peroxides).

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