Which acid of each pair shown here would you expect to be stronger? (i) CH_3CO_2H or CH_2FCO_2H (ii) CH_2FCO_2H or CH_2ClCO_2H (iii) CH_2FCH_2CH_2CO_2H or CH_3CHFCH_2CO_2H (iv)

Which acid of each pair shown here would you expect to be stronger? (

1.	Which acid of each pair shown here would you expect to be stronger? (i) CH_3CO_2H or CH_2FCO_2H (ii) CH_2FCO_2H or CH_2ClCO_2H (iii) CH_2FCH_2CH_2CO_2H or CH_3CHFCH_2CO_2H (iv)
Answer» Solution :(i) `FCH_2CO_2H` is stronger than `CH_3CO_2H` DUE to - I - effect and stablisation of the carboxylate ion of `FCH_2CO_2H` as shown below: (ii) Due to much stronger I-effect of F than Cl, the `FCH_3COO^(-)` ion is much more stable than `ClCH_2COO^(-)` ion. Protons are released in greater CONCENTRATION in `FCH_2COOH`. Hence, `FCH_2COOH` is a stronger acid than `ClCH_2COOH`. (iii) Inductive effect decreases with distance , therefore, -I-effect of F is a stronger in 3-fluorobutanoic acid than in 4-fluorobutanoic acid. Hence, `CH_3CHICH_2COOH` is a stronger acid than `FCH_2CH_2CH_2COOH`. (iv) Therefore due to greater STABILITY of `F_3C - C_6H_4 - COO^(-)` (p) ion over `CH_3 - C_6H_4COO^(-)` (p) ion, `p - F_3C - C_6H_4-COOH` is a much stronger acid than `p - CH_3-C_6H_4 - COOH`.