Question

How do resonance structures affect acidity?

Answer 1

Hint: The acidity of the compound can be examined by their corresponding conjugate base. The base that shows resonance delocalization of the electron pair which is shared by the proton is less basic in nature than the base with no delocalization of electron pair.

Complete step by step answer:
The resonance is shown by the molecule when the one structure cannot describe the single Lewis structure. The resonance may delocalize the electron pair which the base can use to form chemical bonds with the proton. The delocalization increases the stability of the base. The greater is the stability of base, the lower is the reactivity. The base that possesses resonance delocalization of the electron pair which is shared by the proton is less basic than the base with no delocalization. As we know, the weaker base has stronger conjugate acid, thus the compound whose conjugate base which shows resonance stabilization will be more acidic in nature.
For example, in ethanol and acetic acid the deprotonation of ethanol results in ethoxide ions which show no resonance and the deprotonation of the acetic acid results in acetate ions which show resonance structure. As acetate ion has the resonance which delocalizes the electron pair shared by the proton and ethoxide ion does not, therefore acetate ion is weaker base than ethoxide ion. Thus, acetic acid is a stronger acid as compared to ethanol.

Note:
The resonance is shown by those compounds which can possess more than one Lewis structure. The compound which has only one Lewis structure shows no resonance effect.