MCAT Organic Chemistry Question 48: Answer and Explanation

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Question: 48

3. Rank the following in order of decreasing electrophilicity: CR3+, CH3OH, CH3OCH3, CH3Cl

  • A. CH3OCH3 > CR3+ > CH3OH > CH3Cl
  • B. CR3+ > CH3OH > CH3OCH3 > CH3Cl
  • C. CH3OCH3 > CH3Cl > CR3+ > CH3OH
  • D. CR3+ > CH3Cl > CH3OH >CH3OCH3

Correct Answer: D

Explanation:

Good electrophiles are positively charged or polarized. CR+3 is a tertiary carbocation; it has a positive charge, which makes it very electrophilic. CH3Cl and CH3OH are both polarized; however, the leaving groups differ between these two. Cl is a weaker base than OH (HCl is a stronger acid than H2O). As such, Cl will be more stable in solution than OH, which increases the electrophilic reactivity of CH3Cl above CH3OH. CH3OCH3 has a much less stable leaving group, CH3O, and is therefore significantly less electrophilic.

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