I just came across this question in my revision.

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I selected (A) but the correct answer is (D).

Could someone explain where I am going wrong?

  • I is least stable --> most reactive --> most basic
  • Cl is more electronegative than F so III will have a stronger inductive stabilization effect --> III is more stable than II --> III is less reactive than II --> III is less basic than II
  • Hence, rank order: I, II, III
  • 1
    $\begingroup$ You might want to review the electronegativities of F and Cl. $\endgroup$ – Ivan Neretin Feb 22 '19 at 6:31
  • $\begingroup$ From an instructive perspective, it would be nice to see an answer including the pKa all three compounds determined under shared conditions (for the the same solvent); especially for the comparison II vs. III, though. $\endgroup$ – Buttonwood Feb 22 '19 at 21:18

Solution: I had the electronegativity of F vs Cl the wrong way round.

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