The polar mechanism for the nitration of benzene with nitronium ion: ab initio structures of intermediates and transition states.

The nitration of benzene by nitronium ion in the gas phase has been re-examined. New features have been revealed; in particular, three transition states have been detected along the reaction coordinate. These have been shown by IRC analysis to connect an initially formed π complex (pi1) to a σ complex (sig1) (via ts1), sig1 to sig2 (via ts2), and finally sig2 to the product (via ts3). Sig2 also connects to another isomeric σ complex sig3 (via sig23ts), which connects to sig4 (via sig34ts).