Question

What is the carbon-carbon bond length in benzene?
A. \[{\text{1}}{\text{.20}}{{\text{A}}^o}\] and \[{\text{1}}{\text{.31}}{{\text{A}}^o}\]
B. \[{\text{1}}{\text{.39}}{{\text{A}}^o}\]
C. \[{\text{1}}{\text{.39}}{{\text{A}}^o}\] and \[{\text{1}}{\text{.20}}{{\text{A}}^o}\]
D. \[{\text{1}}{\text{.20}}{{\text{A}}^o}\]

Answer 1

Hint:Consider the nature of carbon-carbon bonds present in benzene rings, whether they are single bonds or double bonds. Also consider the effect of resonance (aromaticity) on these bonds.

Complete answer:
Benzene is a cyclic, planar molecule with \[\left( {4n + 2} \right)\pi \] electrons that are delocalized over a ring of six carbon atoms. Thus, benzene obeys Huckel’s rule and is aromatic. This gives some special properties to benzene rings that are peculiar of aromatic compounds.
Benzene has alternate carbon-carbon single bonds and carbon-carbon double bonds. However due to resonance (aromaticity) the pi electrons of carbon atoms are delocalized over the entire ring. Due to this, the carbon-carbon single bonds get some partial double bond character and the carbon-carbon double bonds are also left with partial double bonds. Due to this, all the carbon-carbon bonds in benzene are identical. In benzene, all the carbon-carbon bond lengths are the same. They are equal to \[{\text{1}}{\text{.39}}{{\text{A}}^o}\]

Hence, the correct option is the option (B).

Additional information:
Due to aromatic character, benzene does not undergo typical additional reactions of alkenes. Instead, benzene undergoes electrophilic aromatic substitution reactions.

Note:
 The carbon-carbon single bond has greater bond length than the carbon-carbon bond having partial double bond character. The carbon-carbon bond having partial double bond character has greater bond length than the carbon-carbon double bond.