Fundamentals of Organic ChemistryChemistryGeneral Organic Chemistry
Which of the following compounds will evolve CO ₂ gas upon reaction with an aqueous solution of NaHCO ₃ ? (i) (ii) (iii) (iv) (v)
Options
- A(iii), (iv), and (v)
- B(i), (iii), (iv), and (v)
- C(i), (iii), and (iv)
- D(i), (ii), (iii), (iv), and (v)
Correct answer
D. (i), (ii), (iii), (iv), and (v)
Step-by-step solution
For a compound to evolve CO ₂ gas upon reaction with an aqueous solution of NaHCO ₃ , it must be a stronger acid than carbonic acid ( H ₂ CO ₃ ), which has a pK_a of approximately 6.4 . (i) Croconic acid is highly acidic ( pK_a 0.8 ) because its conjugate base is a highly resonance-stabilized aromatic dianion. It is stronger than H ₂ CO ₃ . (ii) 2,4-Dinitrophenol has two strongly electron-withdrawing - NO ₂ groups that stabilize the phenoxide ion, making it significantly acidic ( pK_a 4.1 ). It is stronger than H ₂