Question

Arrange the following compounds in the increasing order of their property as indicated:
i. Acetaldehyde, acetone, di-tert-butyl ketone, methyl tert-butyl ketone (reactivity towards HCN).
ii. `CH_(3)CH_(2)CH(Br)COOH, CH_(3)CH(Br)CH_(2)COOH, (CH_(3))_(2)CHCOOH, CH_(3)CH_(2)CH_(2)COOH` (acidic strength).
iii. Benzoic acid, 4-nitrobenzoic acid, 3,4-dinitro-benzoic acid, 4-methoxybenzoic acid (acidic strength).

Answer 1

(a) `CH_(3)-overset(CH_(3))overset(|)CH-COOHltCH_(3)CH_(2)CH_(2)COOHltCH_(3)-underset(Br)underset(|)CH-CH_(2)-COOHltCH_(3)CH_(2)-underset(Br)underset(|)CH-COOH`
The magnitude of +I effect of isopropyl group is more than that of n-propyl group. Therefore `(CH_(3))_(2)CHCOOH` is a weaker acid than `CH_(3)CH_(2)CH_(2)COOH`. Now-I effect is less in `CH_(3)CHBrCH_(2)COOH` than in `CH_(3)CH_(2)CHBrCOOH`. In the light of these observations, the increasing order in acidic strengths is justified.

Methoxy `(OCH_(3))` group with +I effect decreases the acidic strength while nitro `(NO_(2))` group with -I effect increases the acidic strength. In the light of these observations, the increasing order of acidic strengths is justified.