| Abstract
| - We report a theoretical study, based on ab initio molecular dynamics simulations in water solution, of themechanism of base-induced β-elimination reactions in systems activated by the pyridyl ring, with halogenleaving groups. The systems investigated represent borderline cases, where it is uncertain whether the reactionproceeds via a carbanion intermediate (E1cb, AxhDH + DN) or via the concerted loss of a proton and thehalide (E2, ANDEDN) upon base attack. Recent theoretical and experimental evidence points toward the lackof a net distinction between the E1cb and E2 reaction paths, which seem to merge smoothly into each otherin these borderline cases (Alunni, S.; De Angelis, F.; Ottavi, L.; Papavasileiou, M.; Tarantelli, F. J. Am.Chem. Soc.2005, 127, 15151−15160). In this study, we explore the dynamics on the potential energy surfacefor the reaction of 2-(2-fluoroethyl)-1-methyl pyridinium with OH- by means of Car−Parrinello simulationsin water solution. Our results indicate that the reaction mechanism effectively evolves through the potentialenergy region of the carbanion: the carbon−fluoride bond breaks only after the carbon−hydrogen bond,confirming the conclusions of a recently reported study of the potential energy surface for this system.
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