resonance forms! ahhhh

[Kirsty_B]

Hey hey! i would really appreciate anyones help if they can help me with this Q?

its..

Explain with reference to reactivity and orientation and using resonance forms, how chlorobenzene behaves when it is treated with bromine in the presence of ferric bromide

thanks guys! x

[Dan the Chemist]

Ok, ferric bromide is your lewis acid, which co-ordinates to the Br2, polarising the Br-Br bond, which is basically a source of 'Br+'.

1. Relative to the reaction with benzene, this reaction will be slower (inductive withdrawal of electron density from the ring by chlorine =>the ring's nucleophilicity is decreased)

2. Expect ortho and para substitution - if you draw the carbocation intermediate of ortho and para substitution, you will see that it has 4 resonance structures (remember pi donation by Cl), but the intermediate in meta substitution only has 3 resonance structures (cannot be stabilised by pi donation from Cl)

Look up 'substituent effects' in any general organic textbook.