Chapter 11, Problem 71FP

Furan, ${\text{C}}_{\text{4}}{\text{H}}_{\text{4}}\text{O}$ , is a substance derivable from oat hulls, corn cobs, and other cellulosic waste. It is a starting material for the synthesis of other chemicals used as pharmaceuticals and herbicides. The furan molecule is planar and the C and O atoms are bonded into a five-membered pentagonal ring. The H atoms are attached to the C atoms. The chemical behavior of the molecule suggests that it is a resonance hybrid of several contributing structures. These structures show that the double bond character is associated with the entire ring in the form of a $\pi$ electron cloud.

a. Draw Lewis structures for the several contributing structures to the resonance hybrid mentioned above.

b. Draw orbital diagrams to show the orbitals that are involved in the $\alpha$ and $\pi$ bonding in furan. [Hint: You need use only one of the contributing structures, such as the one with no formal charges.]

c. How many $\pi$ electrons are there in the furan molecule? Show that this number of $\pi$ electrons is the same, regardless of the contributing structure you use for this assessment.