Substituent effects on the reactions of aromatic triflones with para‐X‐anilines in methanol: Low intrinsic reactivity and transition state imbalances

A kinetic study is reported for S N A r reactions of 2,4,6‐tris(trifluoromethanesulfonyl) anisole 1a with a series of para‐X‐substituted anilines 2a–e in a methanol solution at various temperatures. The substituent effects on free energy (Δ ≠ G ), enthalpy (Δ ≠ H ), and entropy (Δ ≠ S ) of activation are examined. Aniline addition to triflone 1a is characterized by a β X =0.57, α Z =0.31, and an imbalance of I = α Z –β X =−0.26. The imbalance shows that resonance development lags behind CN bond formation at the transition state. Interestingly, analysis of the results in terms of Marcus theory reveals that these S N Ar are associated with some extremely low intrinsic reactivity (log k o =−1.25& © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 255–262, 2011