question_answer 20)

Arrange the following compounds in increasing order of their property as indicated: (i) Acetaldehyde, acetone, di-tert-butyl kentone, methyl tert-butyl ketone (reactivity towards HCN). (ii)  (acid strength). (iii) Benzoic acid, 4-nitrobenzoic acid, 3,4-dinitro benzoic acid;4-methoxy benzoic acid (acid strength).   (i) Greater the   steric hindrance, lesser the reactivity of carbonyl compound towards nucleophilic addition, i.e., towards HCN. (ii) Presence of electron donating group (EV^G) makes an acid more acidic. As the distance between EWG and ?COOH increases, aciditydecreases. (iii) Same as (ii).  

Answer:

(i) The reactivity of a. compound depends on the sterichindrance due to the groups present around the carbonyl group.Greater the steric hindrance, less will be the reactivity of thecompound. Reactivity towards HCN is in following order. Di-tertiary butyl ketone < Methyl tertiary butyl 1-retorie < Acetone< Acetaldehyde. (ii) Alkyl group with effect decreases the acidic strength whereaswith effect increases the acidic strength -I effect decreases withdistance. Increasing order of acidic strength is Increasing order of acidic strength is (iii) Electron donating group  decreases the acidic strength whereas electron withdrawing group  increases the same. Increasing order of acidic strength is: 4-methoxy benzoic acid < benzoic acid < 4-nitrobenzoic acid<3,4-dinitrobenzoic acid.