The Sn Mechanism in aromatic compounds. 24. The positional order of inductive effects in the aromatic ring.

Abstract

The two main views on the transmission of the inductive (I) effect within the ring are tested by comparison of the reactivity of the chlorine in 2-, 3-, and 4-chloro-N-methylpyridinium salts with sodium p-nitrophenoxide in absolute methanol. Activation by the ring N+, corresponding to C^б+ for attached -I groups, is shown to be in the positional order : 2>4>>3. The corresponding rate ratios (at 50 °C) are 4.89 x 10⁷ : 1.62 x 10⁶ : 1. These results strongly favour the view that both σ- and π-electron systems are involved in the intra-annular transmission. Similar results are obtained for reaction with sodium methoxide in absolute methanol.