Multi Transition States for SN2 Reaction in Intramolecular Processes

Abstract

The DFT calculation results for ring-closing reactions of eight different ω–bromoalkanecarboxylate anions, 1-8, five different 4-bromobutylamines, 9-13 and four β–aminoethyl chlorides, 14-17 reveal that the intramolecular substitution nucleophilic attack of the nucleophile (-O- or –NH2) on the electrophilic center (-(CH2)-Br or - (CH2)-Cl) involves multi - transition states. Further, the results establish that the activation energy (∆∆G‡) for intramolecular cyclization processes calculated from the higher transition state is strongly correlated with the experimentally intramolecular cyclization rate (log kintra), whereas the difference in the energies of the highest and the lowest energy transition states is found to correlate strongly with the experimental or MM2 calculated strain energy of the reactant or the strain energy difference between the cycle formed and the reactant (Es Exp). The latter result is the first to predict strain energy based on energy barrier