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Question:

Arrange the following nucleophiles in the decreasing order of nucleophilicity: (A) CH₃C(=O)⁻O⁻ (B) CH₃O⁻ (C) CN⁻ (D) Ref. image

D , C , B , A

B , C , A , D

C , B , A , D

A , B , C , D

Solution:

Conjugate base (nucleophile) is strong if acid is weak and vice-versa.
A) CH₃C(=O)⁻O⁻ is a conjugate base of CH₃C(=O)OH (I).
B) CH₃O⁻ is a conjugate base of CH₃OH (II).
C) CN⁻ is a conjugate base of HCN (III).
D) p-H₃C-C₆H₄-SO₂⁻O⁻ is conjugate base of p-H₃C-C₆H₄-SO₂⁻OH (IV).
Order of acidic nature is IV > I > III > II.
Hence, the decreasing order of nucleophilicity is B > C > A > D.