Question

Arrange the following compounds in increasing order of their property as indicated:
(i) $F-C{{H}_{2}}COOH$,${{O}_{2}}N-C{{H}_{2}}COOH$,$C{{H}_{3}}COOH$,$HCOOH$-acid character
(ii) Acetone, Acetaldehyde, Benzaldehyde, Acetophenone -reactivity towards addition of HCN

Answer 1

The compound which has more ability to release the ${{H}^{+}}$ ions will have a greater acid character. It is found that the electron withdrawing groups increase the reactivity towards addition of HCN.

Complete step by step answer:
(i) the order of acidic character will be:
- As we know that the electron withdrawing ability is:- $N{{O}_{2}}>{{F}^{-}}>H>C{{H}_{3}}$
- The presence of an electron withdrawing group, a compound will show – I effect (It is an effect in which the electron withdrawing group withdraws electrons from adjacent carbon, which will ease the dissociation of OH bond and due to which hydrogen can be easily liberated and hence, acidity increases.), and will show more acidic character.
Hence, the order of acidic character will be: $C{{H}_{3}}COOH$< $HCOOH$< $F-C{{H}_{2}}COOH$< ${{O}_{2}}N-C{{H}_{2}}COOH$
(ii) The increasing order of reactivity towards addition of HCN will be:
- As we know that the addition of HCN is a nucleophilic addition reaction.
- The presence of an electron withdrawing group in a compound will show – I effect and this increases the reactivity towards nucleophilic addition reaction of HCN. While electron donating groups in a compound will show + I effect decreases the reactivity towards nucleophilic addition reaction.
- It is found that the +I effect is more in case of ketones like in acetone, because of the presence of two alkyl groups as compared to aldehydes that contain only one alkyl group. And hence, ketone will be least reactive towards addition of HCN.
- Benzaldehyde doesn’t favour nucleophilic addition reaction because of resonance stabilisation.
- Hence, the increasing order of reactivity will be-
Acetophenone
Note:
- We can say that due to the presence of an electron withdrawing group, a compound will show – I effect, due to which the acidic character increases.
- Compounds that will show - I effect will show the highest nucleophilic addition reaction. Due to -I effect the electron withdrawing group withdraws electrons from adjacent carbon, due to which hydrogen can be easily liberated and hence, acidity increases.