To study the energetics and mechanism of these reactions, the ωB97XD 16 /Def2-SVPD 17 /SCRF 18 =dichloromethane solvent density functional procedure was selected 19 as computationally more feasible than coupled-cluster methods such as CCSD(T) for computing large species such as galvinoxyl and for evaluating intrinsic reaction coordinates (IRCs). This DFT method was first calibrated against both the CCSD(T) 20 /Def2-TZVPPD model and experiment (Table ). This revealed that the relative energy of free C⩸C itself is predicted to be too high by ~28 kcal mol -1 using the ωB97XD/Def2-SVPD/SCRF=DCM method. Transition states were verified using IRC pathways. A model 1,2-substitution reaction which is similar to the reactions shown in Figure and which allows the CCSD(T) level transition state to be located using symmetry alone (C2h) was selected for calibration (Eqn. 2).