CBSE Class 12 · 2008 · Foreign · Aldehydes Ketones and Carboxylic AcidsShort Answer

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State reasons for the following situations:
i) Monochloroethanoic acid is a weaker acid than dichloroethanoic acid.
ii) Benzoic acid is a stronger acid than ethanoic acid.

Solution

(i) Acidity rises with the stabilisation of the carboxylate. Two chlorines withdraw more electron density than one, so CHCl

_{2}

COO

^{-}

is more stabilised than CH

_{2}

ClCOO

^{-}

— dichloroethanoic acid is the stronger acid.
(ii) In benzoic acid the ring carbon (sp

^{2}

) exerts a −I pull and the benzoate charge is partly delocalised; in ethanoic acid the +I methyl pushes electrons onto the carboxylate. Hence C

_{6}

_{5}

COOH > CH

_{3}

COOH in acid strength.

CBSE Class 12 Board · 2008 · Foreign · Subjective

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