GROUND-STATE VS TRANSITION-STATE SUBSTITUENT EFFECTS ON REACTIONS OF AZIRIDINIUM SALTS

The possibility that the similarity of Hammett rho values for several very different reactions of 2-arylaziridinium salts is due to ground state effects was investigated by MO methods and ESCA. Minimum energy structures of p-nitrophenyl-, phenyl-, and p-methoxyphenyl-substituted ions, however, have the same C2-N bond lengths. This result shows that substituent effects are primarily a transition state phenomenon, even in the three-membered ring heterocycles. In agreement, the ground state does not have significant amino carbocation character based on similar charge distributions of 2-phenyl-NN-dimethylaziridinium ion and N,N,N-trimethylbenzylammonium ion as well as the same nitrogen Is binding energies by ESCA studies on corresponding salts.