Which of the following acids has the smallest dissociation...

Which of the following acids has the smallest dissociation constant?
(a) $\mathrm{FCH}_{2} \mathrm{CH}_{2} \mathrm{COOH}$
(b) $\mathrm{CH}_{3} \mathrm{CHFCOOH}$
(c) $\mathrm{BrCH}_{2} \mathrm{CH}_{2} \mathrm{COOH}$
(d) $\mathrm{CH}_{3} \mathrm{CHBrCOOH}$

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Key Concepts

Substituent Electronegativity and Position

The influence of a substituent on acid strength is governed largely by its electronegativity and its proximity to the carboxyl group. Highly electronegative substituents at positions closer to the carboxyl group (such as alpha or beta positions) exert a stronger inductive effect, stabilizing the conjugate base more effectively than those that are farther away, which results in an increased acid strength.

Acid Dissociation Constant (Ka)

The acid dissociation constant, Ka, quantitatively measures the strength of an acid in solution. It represents the equilibrium constant for the dissociation of an acid into its conjugate base and proton. A smaller Ka indicates a weaker acid, meaning it dissociates less and produces fewer hydrogen ions.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating influence exerted by substituents through sigma bonds. Electron-withdrawing groups reduce electron density on the molecule, stabilizing the conjugate base and thereby increasing the acid's strength. The magnitude of this effect depends on the substituent's electronegativity and its distance from the acid functional group.

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