Question

Explain the resonance structure of benzoic acid.

Answer 1

Resonance:

• The ability to move pi electrons in the system is called Resonance.
• The Lewis structure that can describe the delocalization of electrons in a polyatomic ion or a molecule is called Resonance structure.

Resonance in benzoic acid:

• The formula of Benzoic acid is ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH}$.
• The Carboxylic acid functional group $\left(-\mathrm{COOH}\right)$ is a strong electron-withdrawing group.
• When Carboxylic acid gets attached to the Benzene ring and withdraws electron density from Benzene to produce positive sites at ortho and para positions, thus the Benzoic acid produces resonating structures.

Resonating structures:

• Structure 1 - The $\mathrm{C}=\mathrm{O}$ bond of the Carboxylic group breaks, Oxygen gets the negative charge and Carbon gets the positive charge then, new pi-bond forms between the second Carbon and the functional group.
• Structure 2 - The pi-bond between the fifth and sixth Carbon atoms breaks and a new pi-bond forms between the sixth and first Carbon atoms.
• Structure 3 - The pi-bond between the third and fourth Carbon atoms breaks and a new pi-bond forms between the fourth and fifth Carbon atoms.
• Structure 4 - The pi-bond between the second Carbon and the functional group breaks and a new pi-bond forms between the second and third Carbon atoms
• Structure 5 - The pi-bond forms between Carbon and Oxygen in the functional group