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(i) How inductive effect helps to explain reactivity and acidity of carboxylic acids? (ii) HCOOH is more acidic than CH_(3)COOH. Why? |
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Answer» Solution :(i) Reactivity of carboxylic acid: 1. When a highly electronegative atom such as halogen is attached to a carbon then it makes the C-X bond polar. 2. In such CASES the -I effect of halogen facilitates the attack of an incoming nucleophile at the polarized carbon and hence INCREASES the reactivity.  3. If a -I group is attacher neared to a carbonyl carbon, it decreases the availability of electron density on the carbonyl carbon and hence increases the rate of the nucleophilic addition reaction. Acidity of carboxylic acid: 1. When a halogen atom is attached to the carbon which is neared to the carboxylic acid group, its -I effect withdraws the bonded electrons towards itself and makes the ionization of `H^(+)` easy. 2. The acidity of various chloro acetic acid is in the following order. `Cl_(3)C-COOH gt Cl_(2)CHCOOH gt ClCH_(2)COOH` The strength of the acid increases with INCREASE in the -effect of the group attached to the carboxyl group. 3. Similarly the following order of acidity in the carboxylic acids is due to the +I effect of alkyl group. `(CH_(3))_(3)C COOH lt (CH_(3))_(2)CHCOOH lt CH_(3)COOH`. (ii) `underset(("formic acid"))(H-overset(O)overset(||)(C)-O-H)""underset(("Acetic acid"))(CH_(3)-overset(O)overset(||)(C)-O-H)` Out of acetic acid and Formic acid, formic acid is conidered stronger because, `CH_(3)` group in acetic acid contributes electron density towards the O-H bond, making it harder to remove the `H^(+)` ion and making acetic acid a WEAKER acid that formic acid. `therefore`Formic acid is more acidic one. |
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