We conducted analyses on the energy barriers associated with C-C bond formation and the spin-density obtained from natural bond orbital (NBO) population analysis of the spectator atoms, Fe, in case of Fe 2 M and M' in case of M' 2 Ni, in the intermediate C to elucidate the interdependencies between these parameters (Figure ). The plot reveals a distinct reverse correlation: an escalation in the energy barrier from Sc to Ti in Fe 2 M coincides with the reduction in the natural spin densities on the two Fe atoms. Further, a decrement in the energy barrier for Fe 2 V is accompanied by an augmentation in spin density, which progressively increases from Fe 2 V through Cr to Mn with a decreasing trend for energy barriers. Further, a decrement in the energy barrier for Fe 2 V is accompanied by an augmentation in spin density, which progressively increases from Fe 2 V through Fe 2 Cr to Fe 2 Mn with a decreasing trend for energy barriers. Upon reaching Fe 3 , there is an increment in the energy barrier, accompanied by a marginal reduction in spin density, albeit not to a significant extent followed by an increase in spin density concomitant with reduced energy barriers.