Question

Draw all the possible resonance structures of benzaldehyde.

Answer 1

Hint:
Resonance structures of benzaldehyde are formed due to the electronegativity of oxygen and the delocalised electrons of benzene ring. There are in total four resonance structures. The structures contain a negative charge on oxygen and positive charge on the carbon present in the benzene ring.

Complete step by step answer:
Resonance is the phenomenon where in a compound an possess different configurations with respect to their skeletons due to the delocalized electrons that are present in the benzene ring and the electronegativity of the surrounding atoms.

This electronegativity leads to the attraction of a pair of electrons from the benzene ring and towards the atom that has high electronegativity as in the case of oxygen in this question.
The resonance structures all have the same energy as each other. But there is a difference in energy between the first structure of the picture above and the other resonance structures. This difference is called resonance energy.
The more resonance structures a compound has the more stable it is.
The resonance structures are transient and the delocalized electrons are constantly moving.
The resonant energy is always negative.
Most resonant structures contribute equally to the resonance hybrid but in some cases some resonant structures may contribute more to the hybrid than others. This can happen if some of the resonant structures have the greatest number of octets and if they have the least number of formal charges the atoms present in the structure.
In Benzaldehyde, we can see that oxygen gets negative formal charge and thus an extra pair of electrons from the double between carbon and oxygen. This leads to a double bond forming between carbon of the carbonyl group and the carbon in the benzene structure.

Note: Remember that the greater number of resonating structures that a compound has the more stability it possesses.
-The delocalized electrons move towards the atom that possesses a negative formal charge.
-Resonant structures are always transient meaning it exists for a short period of time.