Question

What is a resonance hybrid? Give one example.

Answer 1

Resonance

• In the valence bond theory, resonance is also known as mesomerism
• Resonance is a way of defining bonding in particular molecules or polyatomic ions by combining many contributing structures into a resonance hybrid.

Resonance Hybrid

• A molecular structure is a combination of two structures with different pie bond electron positions.
• As the 'average' of the contributing structures, the resonance hybrid represents the actual molecule.

Example

• Benzene is an aromatic hydrocarbon.
• The molecular formula of benzene is ${\mathrm{C}}_6{\mathrm{H}}_6$.
• Benzene generally contains a cyclic structure in which molecules are designed in such a way that it contains alternating single and double bonds with respect to their nearby carbon atoms.
• Each carbon atom has a hydrogen atom linked to it.
• There are two probable benzene resonance configurations which are shown by rotating the bonds and resonance hybrid the structure which is equivalent to both structures are shown below:

Benzene show resonance due to the presence of pi bonds which take part in delocalization and gives resonating structures. This delocalization causes each carbon-carbon bond to have a bond order of 1.5, implying that they are stronger than regular C-C sigma bonds.