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).

Explanation

(I) the reactivity towards HCN addition decreases as +1 effect of alkyl group ( or groups ) increases and / or the hindrance to the nuclephilic attack by `CN^(-)` at the carbonyl carbon increases .

(ii ) we known that + I effect decreases the acid strength of carboxylic acid while -1 effect increases the acid strength of carboxylic acid . the +I effect of isopropyl group ism more than of n- propyl , therefore the`CH_3 underset(CH_3) underset(|) CHCOOH ` is a weaker acid than `CH_3 CH_2 CH_2 COOH .`
since -I effect decreases with distance therefore `CH_3 CH_2 (Br ) COOH ` is a stronger acid than `CH_3 CH (Br) CH_2 COOH `
Thus the overall increasing order of acid strength is
`CH_3 underset(CH_3) underset(|)CH-COOH lt CH_3CH_2 CH_2 COOH lt CH_3 underset(Br) underset(|) CHCH_2COOH lt CH_3CH_2 underset(Br)CH - COOH `
(iii ) electron donating group decrease the acid strength and therefore 4-methoxy benzoic acid is a weaker acid than benzoic acid
since electron withdrawing groups increases the acid strength therefore both 4- nitrobenzoic acid and 3,4 dinitrobenzoic acids are stronger acids than benzoic acid further because of the presence of additional `-NO_2` group at m - position w.r.t -COOH group , 3,4 dinitrobenzoic acid is little is a little stronger acid than 4- nitrogent acid thus the increasing order of acid strength is
4 - methyoxybenzoic acid < benzoic acid < 4- nitrobenzoic acid < 3,4 -dinitrobenzoic acid .