Geometrical and kinetic isotope effects on SN2 chemical reactions using multi-component molecular orbital method

To estimate the kinetic isotope effect (KIE) for nucleophilic substitution (SN2) reaction, F− + CH4 → CH3F + H−, and deuterated ones, we have considered the geometrical isotope effect (GIE) induced by the difference of the protonic and deuteronic wavefunctions using the multi-component molecular orbital (MC_MO) method. By replacing protons with deuterons, the C–D bond lengths are about 0.007 Å shorter than C–H. We estimated the ratio ( k a H / k a D ) of rate constants based on MC_MO results. The geometrical and energetic differences between H and D compounds are induced by relaxation of electronic structures due to the difference in the wavefunctions of the proton and deuteron.