3.2.3 MDA reaction on 6-5 double bond of C60:
As shown in Figure S4 , for 6-5 also, the energy release
associated with A16-5S formation (-4.3
kcal/mol) is noticed to be comparable enough with its ‘Direct’
counterpart. The transition state
(TS16-5S) for
R16-5S formation requires nearly 10.8
kcal/mol higher energy than its 6-6 analogue. The enthalpy change
associated with R15-6S production is
observed to be -13.6 kcal/mol, inferring the thermodynamic viability of
the second DA reaction through the ‘Alternative’ approach. In the third
DA reaction, A26-5S needs 27.4
kcal/mol activation energy (TS16-5S)
for R26-5 formation, which is not only
9.4 kcal/mol higher than its 6-6 counterpart but also 4.2 kcal/mol
higher than the corresponding barrier obtained in the ‘Direct’ approach.
This reaction step is also exothermic, just like the previous DA steps,
with the associated reaction enthalpy value of -10.7 kcal/mol. For the
fourth DA reaction, the pathway will be exactly identical with the one
established for 6-5 bond in the ‘Direct’ approach.
Similar to the ‘Direct’ approach, in this case also, asynchronicity
arises in the third and fourth TSs as the difference of C-C bond lengths
is 0.2 and 0.4 Å, respectively (Figure S3 ).