Phenol Resonance

Resonance is a phenomenon that is known to stabilize structures. It is why the cyclic aromatic structure of benzene is so stable.

The more resonance structures you can draw for a molecule, the more stable it is.

Take the resonance of phenol for example:

Figure 1: Phenol resonance mechanism

As seen with the conjugation of furan, the oxygen atom with its aligned p-orbital and lone pair of electrons can participate in resonance.

The resonance structure begins at the oxygen's lone pair of electrons. Here the oxygen atom is acidic because it allows the electrons to travel through the aromatic system.

Notice in the final structure, the aromaticity of the ring has been restored as well as returning the full original structure of phenol.

The charges of resonance structures are also very important. No electrons are gained or lost as it is just the electrons traveling around the structure. This means the overall charge of all resonance structures must be the same as the structure you began with.

For example, phenol has a neutral charge, therefore all resonance forms must have a neutral charge. As you can see in the mechanism, the resonance forms have a +1 charge on the oxygen atom and a -1 charge on a carbon atom. Overall, the charge is 0. This is another way to ensure your resonance structures are correct.