3.1.2 MDA reaction on 6-6 double bond of Li+@C60:
To check the effect of Li+ encapsulation on MDA reaction, we have explored all three steps associated with the MDA reaction on 16-6L. It has been well-established that the encapsulation of Li+ enhances the reactivity of 6-6 double bond of fullerene towards DA reactions and yields mono-functionalized fullerene as the first DA product[46 ]. Here, we intend to examine whether the effectiveness of Li+ encapsulation during MDA reaction associated with the 6-6 double bonds persists or not. The second DA reaction originated from A16-6OL (Figure 3 ) is observed to be 7.8 kcal/mol more stable than the initial reactants. The activation barrier associated with the conversion of A16-6OL to R16-6OLvia TS16-6OL is found to be 11.7 kcal/mol, which is 4.0 kcal/mol lower in energy than its neutral counterpart. The enthalpy change involves in R16-6OLformation is -29.0 kcal/mol, which is ~1.0 kcal/mol lower than its R16-6O fabrication. So, it can be articulated that Li+-encapsulation successfully enhances the reactivity of encapsulated fullerene towards the second DA reaction by reducing the activation barrier. As evident from Figure 3 , the third DA reaction is initiated from A26-6OL, which is placed at -44.9 kcal/mol on the PES. The activation barrier associated with TS26-6OL (Figure 2 ) corresponding to R26-6Lformation is found to be 3.6 kcal/mol lower than the neutral C60analogue. The exothermic nature of this step is also noted from the associated enthalpy change of -26.9 kcal/mol with respect to A26-6OL, which is 2.4 kcal/mol lower than that of neutral C60. For the fourth DA reaction, the adduct, A36-6L (stabilized at-76.9 kcal/mol on the PES) generates P46-6Lthrough a transition state, TS36-6L, with a barrier height 14.6 kcal/mol. The end product, P46-6L is -101.8kcal/mol downhill than the starting reactant 16-6L, indicating the entire process to be thermodynamically feasible in nature. In this case, all three steps are also identified as synchronous processes as the newly formed C-C bonds between the fullerene surface and diene in the TSs are calculated to be nearly equal in length.
Thus, from our computational analysis, it is evident that for Li+@C60, all three steps of MDA reactions are more likely to occur both kinetically as well as thermodynamically due to reduced activation barrier and higher exothermicity than its neutral counterpart. So, it can be inferred that Li+ encapsulation significantly affects the reactivity in each step of the 6-6 MDA reaction.