Question

Why does nitrobenzene not undergo friedel craft alkylation?

Answer 1

It is due to the presence of nitro group. It is strong electron-acceptor group. It lowers electron density at the benzene ring and it will no longer react with alkyl cations. Also alkyl cations are not the most reactive electrophiles. Nitro group pulls electrons from the benzene ring, which will then form resonance structures, which also explain the preffered position of electrophilic attack if we use stronger electrophile.