DFT‐PCM Study on Solvolytic Behaviour of N ‐alkyl‐X‐pyridinium Ions

Using the M06‐2X method and IEFPCM for ethanol, geometries of various N ‐benzhydryl‐X‐pyridinium ions and corresponding heterolytic transition structures have been optimized to calculate free energies of activation (▵ G ≠model ) for the model heterolysis of the ions at 25 °C. Very good correlations between ▵G ≠model values and corresponding measured ▵ G ≠ values have made it possible to estimate reliable reactivities of N ‐(4,4′‐dimethoxybenzhydryl)‐X‐pyridinium ions in protic solvents as well as nucleofugality parameters ( N f calc ) for 18 X‐substituted pyridines. Computational results further reveal that geometric progression along the heterolytic reaction coordinate is synchronized with ionic charge transfer. A Leffler‐Hammond coefficient of 0.65 (×100 %) corresponds to both the amount of the ionic charge transferred from the X‐pyridine moiety to the alkyl electrofuge (65–67 %) and the extent of geometric progression (64 %) on proceeding from the ionic substrate to TS in the thermoneutral heterolysis. Consequently, exergonic heterolyses of very reactive N ‐alkyl‐X‐pyridinium ions proceed through the geometrically late transition states.