Write a note on the effect of substituents on the acidic strength of carboxylic acid compounds.

(N/A) Substituents may affect the stability of the conjugate base and thus,also affect the acidity of the carboxylic acids.
$(a)$ Effect of substituents on the acidity of carboxylic acids:
$(i)$ Electron withdrawing groups $(EWG)$ increase the acidity of carboxylic acids by stabilizing the conjugate base through delocalization of the negative charge by inductive and/or resonance effects.
$(ii)$ The effect of the following groups in increasing acidity order is:
$Ph < I < Br < Cl < F < CN < NO_{2} < CF_{3}$
$(iii)$ Thus,the following acids are arranged in order of decreasing acidity (based on $pK_{a}$ values):
$CF_{3}COOH > CCl_{3}COOH > CHCl_{2}COOH > NO_{2}CH_{2}COOH > NC-CH_{2}COOH > FCH_{2}COOH > ClCH_{2}COOH > BrCH_{2}COOH > HCOOH > ClCH_{2}CH_{2}COOH > C_{6}H_{5}COOH > C_{6}H_{5}CH_{2}COOH > CH_{3}COOH > CH_{3}CH_{2}COOH$
$(iv)$ Direct attachment of groups such as phenyl or vinyl to the carboxylic acid increases the acidity of the corresponding carboxylic acid,contrary to the decrease expected due to the resonance effect. For example: $CH_{2}=CHCOOH$ is more acidic than $CH_{3}COOH$.