Q15-15-24 - Organic Chemistry (Mcmurry)

Question

Look at the three resonance structures of naphthalene shown in Section 15-6, and account for the fact that not all carbon-carbon bonds have the same length. The C1–C2 bond is 136 pm long, whereas the C2–C3 bond is 139 pm long

Step-by-Step Solution

Answer

As the C₁ and C₂ bond has a larger double bond contribution in resonance hybrid and is shorter than the C₂ and C₃ bond. Thus, C₂and C₃ bond length is longer than C₁and C₂.

Hence C₁ and C₂   bond is 136 pm long, whereas the C₂and C₃  bond is 139 pm long.

                                  Resonance structures of naphthalene

Naphthalene

Naphthalene is a bicyclic aromatic hydrocarbon with a molecular formula C₁₀H₈. It is a white crystalline solid and is found in coal tar or crude oil.

Three resonance structure

The three resonance structures of naphthalene are as shown:

Resonance structures of naphthalene

The bond between C₁ and C₂ is represented as a double bond in two of the three resonance structures whereas the bond between C₂ and C₃ is shown as a double bond in one resonance structure.

As the C₁ and C₂ bond has a larger double bond contribution in resonance hybrid and is shorter than the C₂ and C₃  bond. Thus, C₂ and C₃  bond length is longer than C₁ and C₂  .

Hence C₁ and C₂   bond is 136 pm long, whereas the C₂ and C₃  bond is 139 pm long.