Question
Give the evidence for the cyclic structure of benzene.
✓
Answer
Evidence for the cyclic structure of benzene:
$i.$ Benzene yields only one and no isomeric monosubstituted bromobenzene $(C_6H_5Br)$ when treated with equimolar bromine in $FeBr_3.$ This indicates that all six hydrogen atoms in benzene are identical.
$\underset{\text { Benzene }}{ C _6 H _6}+ Br _2 \xrightarrow[\text { Bromobenzene }]{ Fe _6} C _6 H _5 Br + HBr$
$ii.$ This is possible only if benzene has cyclic structure of six carbons bound to one hydrogen atom each.
$iii.$ Benzene on catalytic hydrogenation gives cyclohexane.
$\underset{\text { Benzene }}{ C _6 H _6}+3 H _2 \xrightarrow{ Ni } \underset{\text { Cyclohexane }}{ C _6 H _{12}}$
This confirms the cyclic structure of benzene and three $C = C$ in it.
$i.$ Benzene yields only one and no isomeric monosubstituted bromobenzene $(C_6H_5Br)$ when treated with equimolar bromine in $FeBr_3.$ This indicates that all six hydrogen atoms in benzene are identical.
$\underset{\text { Benzene }}{ C _6 H _6}+ Br _2 \xrightarrow[\text { Bromobenzene }]{ Fe _6} C _6 H _5 Br + HBr$
$ii.$ This is possible only if benzene has cyclic structure of six carbons bound to one hydrogen atom each.
$iii.$ Benzene on catalytic hydrogenation gives cyclohexane.
$\underset{\text { Benzene }}{ C _6 H _6}+3 H _2 \xrightarrow{ Ni } \underset{\text { Cyclohexane }}{ C _6 H _{12}}$
This confirms the cyclic structure of benzene and three $C = C$ in it.
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