Question

Compare the acidic strength of propenoic acid, propanoic acid, and propionic acid.

Answer 1

Before answering this question, we should first know On which acidic strength of an acid depends. To choose or compare between the acidic strength of acids, We should know about their ability to donate a proton. Then only we will know which of them has greater acidic strength.

Complete answer:
From the three acids that are given in the question, the acid from which the hydronium ion will be removed faster and will form its carboxylate ion will be proved to have more acidic strength. We have heard about the bent rule in which more is the s character, more is the electronegativity, more will be the electron-withdrawing tendency, more is the carboxylate ion stability.
Firstly, In the case of Propanoic acid, the C atom is attached to the $-COOH$group and ${{H}^{+}}$has to be removed from it. The hybridization is $s{{p}^{3}}$, In this, the s character is 25%.
Then In Propenoic acid, the C atom is attached to the $-COOH$group and ${{H}^{+}}$has to be removed from it. The hybridization is $s{{p}^{2}}$, In this, the s character is 33.33%.
In the case of propionic acid, the C atom is attached to the $-COOH$group and ${{H}^{+}}$has to be removed from it. The hybridization is $sp$, In this the s character is 50%.
In between these three, propionic acid has the greater % of s character, therefore, it will have more electronegativity, and the tendency to withdraw electrons increases.
Therefore, Propionic acid has greater acidic strength than propenoic acid and propanoic acid.

Note:
The molecular formula of Propanoic acid is $C{{H}_{3}}C{{H}_{2}}COOH$, Propenoic acid is $C{{H}_{2}}=CH-COOH$and propionic acid is$CH\equiv C-COOH$. The strength of acid also depends on various factors – The polarity of the bond, the Strength of the bond, etc.