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Which of the following statements is correct?

$\begin{array}{1 1}(a)\;P-NO_2C_6H_4COOH\text{ is less acidic than the meta isomer}\\(b)\;P-NO_2C_6H_4COOH\text{ is more acidic than the meta isomer}\\(c)\;\text{P-chloro benzoic acid is more acidic than its meta isomer}\\(d)\;\text{all above}\end{array}$

1 Answer

In para isomer,the resonance interaction of the $NO_2$ with the ring induces some positive charge on the ring.Carbon bearing the $COO^-$.This induces a strong electron with drawing induce effect with stabilies the base and hence acid-strengthening.
In meta isomer,the positive charge is developed at the carbon ortho to the carbon bearing $COO^-$.Its power to with draw $e^{\ominus}$ from $COO^-$ is less and thus meta isomer is less acidic.
Hence (a) is the correct answer.
answered Feb 26, 2014 by sreemathi.v
edited Feb 26, 2014 by sreemathi.v

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