Fig. 1: Schematic PES of the F− + (CH3)3CI reaction.
From: Unexpected steric hindrance failure in the gas phase F− + (CH3)3CI SN2 reaction

Green curve: back-side attack SN2; Purple: front-side attack SN2; Black: anti-E2; Red: syn-E2. The relative energies obtained from CAM-XYG3/AVTZ(-PP) and CCSD(T)/AVTZ(-PP) (in brackets) methods are all in eV.