Q11 · CSIR NET Chemistry, June 2015
Paper: CSIR NET June 2015 · Subject: Organic Chemistry · Chapter: General Organic Chemistry · Topic: Acidity Basicity · Marks: 2 · Difficulty: Hard
The correct order of pKa values for the compounds X, Y and Z is 
(X) 
(Y) 
(Z)
(X) (Y) (Z)(a)X $>$ Y $>$ Z
(b)$\mathrm{Y}>\mathrm{Z}>\mathrm{X}$
(c)Z $>$ X $>$ Y
(d)Y $>$ X $>$ Z
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Fluorene C–H pKa ≈ 22.6 (Z) > phthalimide N–H ≈ 8.3 (X) > pentacyanocyclopentadiene (Y), a superacid (pKa < −10; aromatic anion stabilised by five CN). Z > X > Y (c).
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