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

Short answer

As the C₁and C₂ bond has a larger double bond contribution in resonance hybrid and is shorter than the C₂and C₃ bond. Thus, C₂and C₃bond length is longer than C₁and C₂.

Hence C₁and C₂ bond is 136 pm long, whereas the C₂and C₃ bond is 139 pm long.

Resonance structures of naphthalene

Step-by-step solution

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 C₂is represented as a double bond in two of the three resonance structures whereas the bond between C₂and C₃is 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 C₂and C₃ bond. Thus, C₂and C₃ bond length is longer than C₁ and C₂ .

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