Q23 E - Chemistry (OpenStax)

Question

Benzene is one of the compounds used as an octane enhancer in unleaded gasoline. It is manufactured by the catalytic conversion of acetylene to benzene: 3C₂H₂  C₆H₆

Draw Lewis structures for these compounds, with resonance structures as appropriate, and determine the hybridization of the carbon atoms in each.

Step-by-Step Solution

Answer

The Lewis structure of benzene is as follows:

Step 1: Definition of Lewis structure

Lewis structure is a molecule's structural representation in which atoms are joined by lines. Covalent bonds are shown by the lines connecting atoms.

Lewis structure of benzene

Step 2: Conversion of acetylene into benzene

Consider the following reaction

 \(\begin{array}{\underline{\phantom{xx}}}3{{\rm{C}}_2}{{\rm{H}}_2}{\rm{   }} \to {\rm{  }}{{\rm{C}}_6}{{\rm{H}}_6}\\acetylene{\rm{    }}benzene\end{array}\)

Acetylene's Lewis structure is as follows:

\begin{aligned}{\underline{\phantom{xx}}}{\rm{H}}-{\rm{C}}\equiv{\rm{C}}-{\rm{H}}\\{\rm{}}acetylene\end{aligned}
 Each carbon atom in acetylene is sp hybridized. Each carbon atom is two sp hybrid orbitals are involved in the creation of sigma bonds with hydrogen and carbon. The two unhybridized half-filled p-orbitals of carbon are important in the creation of pi bonds with other carbon atoms.

Step 3: Resonance structure of benzene

The resonance structure of benzene is as follows:

Resonance structure of benzene

Each carbon atom in benzene is sp² hybridized. Each carbon atom is three sp² hybrid orbitals are involved in the production of a sigma bond with hydrogen and two carbon atoms. One half-filled unhybridized p-orbital of carbon is associated with the formation of pi bonds involving neighboring carbon atoms. Three alternative double bonds are present in the resonance structure of benzene.