Efficiency of electric field catalysis in nucleophilic and electrophilic addition to polyenes

摘要

The energetics of nucleophilic addition of pyridine to polyenes of various lengths and the corresponding protonation of these polyenes by methyl ammonium fluoride was computationally determined using ab initio methods. These reactions were also studied in the presence of an electric field (2.5 and 5MV/cm) oriented along the polyene long axis in the direction which will enhance the reaction. Assuming linearity over a long range, and extrapolating the data for 2.5MV/cm to 10nmchain length gave a reduction in the activation energy of the nucleophilic addition of 7 orders of magnitudes implying a ~10~5 rate enhancement. Conversely, the longer the chain, the smaller is the electric field needed to catalyze the reaction. The transition state locations of the various reactions were determined using the slopes of the Ea versus E0 plots as well as the Marcus α values. It turns out the efficiency of electric field catalysis is a function of the transition state location. The latter is the transition state (more endothermic reaction) and the more efficient is the electric field catalysis.