Fundamentals of Organic ChemistryChemistryGeneral Organic Chemistry
Identify the correct decreasing order of acidic strength for the three indicated protons in the following molecule.
Options
- A(i) > (ii) > (iii)
- B(ii) > (i) > (iii)
- C(ii) > (iii) > (i)
- D(i) > (iii) > (ii)
Correct answer
B. (ii) > (i) > (iii)
Step-by-step solution
The acidic strength of a proton depends on the stability of the conjugate base (carbanion) formed after its removal. Let us analyze the stability of the carbanions formed by the removal of each indicated proton: For proton (i): The carbanion formed is stabilized by resonance ( -M effect) with the adjacent thiocarbonyl ( C=S ) group. For proton (ii): The carbanion formed is highly stabilized by resonance with the adjacent C=S group and is additionally stabilized by the adjacent sulfur atom via its -I effect and the