Q14 · CSIR-NET Chemistry, June 2011
Paper: CSIR-NET June 2011 · Subject: Organic Chemistry · Chapter: General Organic Chemistry · Topic: Acidity Basicity · Marks: 2 · Difficulty: Hard
The correct order of acidity of the following compound $A-C$ is: 
(a)B $>$ C $>$ A
(b)$\mathrm{C}>\mathrm{B}>\mathrm{A}$
(c)A $>$ C $>$ B
(d)A $>$ B $>$ C
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Pentakis(trifluoromethyl)cyclopentadiene (A) is a carbon superacid: five CF₃ groups stabilise the aromatic cyclopentadienide. Pentamethylcyclopentadiene (C, pKa ≈ 26) is next. Cyclopropene (B) is the weakest acid because its conjugate base would be the antiaromatic cyclopropenyl anion. A > C > B.
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