Question

Draw structures 01 conjugate bases of monochloroacetic acid and dichloroacetic acid. Which one is more stabilized by -I effect?

Answer 1

1. $$\underset{\mathrm{Acid}}{\mathrm{CiC}}\mathrm{H}{\phantom{A}}_2-\mathrm{COOH}+\mathrm{H}{\phantom{A}}_2\mathrm{O}\stackrel{-\rightharpoonup }{\leftharpoondown -}\underset{\mathrm{Conjugate}\mathrm{base}}{\mathrm{ClCH}{\phantom{A}}_2-\mathrm{COO}{\phantom{A}}^{-}}+\mathrm{H}{\phantom{A}}_3\mathrm{O}{\phantom{A}}^{+}$$
   ClCH₂COO ^– is a conjugate base of ClCH₂COOH
2. $$\mathrm{Cl}{\phantom{A}}_2\mathrm{CH}-\mathrm{COOH}+\mathrm{H}{\phantom{A}}_2\mathrm{O}\stackrel{-\rightharpoonup }{\leftharpoondown -}\underset{\mathrm{Conjugate}\mathrm{base}}{\mathrm{ClCHCOO}-}+\mathrm{H}{\phantom{A}}_3\mathrm{O}{\phantom{A}}^{+}$$
   ClCHCOO ^– is a conjugate base of Cl₂CHCOOH
3. 
   
   The dichloroacetate ion formed gets stabilised due to electron-withdrawing effect of two chlorine atoms ( – I effect).