The Sn2 Reaction: A Theoretical-Computational Analysis of a Simple and Very Interesting Mechanism

M. CAPURSO; R. GETTE; G. RADIVOY; V. DORN

Congreso; 23th ECSOC; 2019

Abstract: Bimolecular nucleophilic substitution (SN2) reaction is one of the most frequentlyprocesses chosen as model mechanism to introduce undergraduate chemistry students tocomputational chemistry methodology. In this work, we performed a computational analysis forthe ionic SN2 reaction, where the nucleophile charged (X−; X=F, Cl, Br, I) attacks the carbon atom ofthe substrate (CH3Cl) through a backside pathway, and simultaneously, the leaving group isdisplaced (Cl−). The calculations were performed applying DFT methods with the Gaussian09program, the B3LYP functional, the 6-31+G* basis set for all atoms except iodine (6-311G*), and thesolvents effects (acetonitrile and cyclohexane) were evaluated with the PCM model. We evaluatedthe potential energy surface (PES) for the mentioned reaction considering the reactants, theformation of an initial complex between the nucleophile and the substrate, the transition state, afinal complex where the leaving group is still bound to the substrate and the products. We analyzedthe atomic charge (ESP) and the bond distance throughout the process. Gas phase and solventstudies were performed in order to analyze the solvation effects on the reactivity of the differentnucleophiles. We observed that increasing solvent polarity, decreases reaction rates. On the otherhand, we thought it would be enriching, to carry out a reactivity analysis from the point of view ofmolecular orbitals. Therefore, we analyzed the MOs HOMO and the MOs LUMO of the differentstationary states on PES, both in a vacuum (gas phase) and in acetonitrile as the solvent.