Conjugation in Furan

There is conjugation and conjugated double bonds. Are they related?

The answer is yes! Conjugated double bonds are two more double bonds separated by a single bond. Together they participate in conjugation through p-orbitals. This is generally allowed by the planar nature of molecules forming perfect p-orbital alignment for extended molecular orbital hybridization.

The argument here is that it is not necessary that there need to be pi electrons from a double bond participating in what we call Conjugation.

A good example of this is furan.

Figure 1: Furan structure

From the structure, we can immediately identify conjugated double bonds. But are these carbons the only atoms that participate in the conjugated system?

The answer is no. The oxygen atom has a p-orbital also aligned with the carbon's p-orbital, with a lone pair of electrons.

These can indeed participate in the extended hybridization we see stabilizing these structures, and we will see the electrons resonating throughout the structure, not just those 4 carbons in double bonds.