3.1.3 MDA reaction on 6-5 double bond of C60:
The initial adduct, A16-5O formed
between the first DA product (16-5) and butadiene
molecule is found to be stabilized by -4.2kcal/mol than its initial
counterparts. The conversion of A16-5Oto R16-5O involves an activation
height of 26.4 kcal/mol (TS16-5O),
which is 10.7kcal/mol higher than
TS16-6O. Though the thermodynamic
feasibility of the reaction is evident from the exothermicity value of
9.4 kcal/mol, the resultant product,
R16-5O is found to be 18.8kcal/mol
less stable than its 6-6 fabrication. The subsequent adduct for third
functionalization, A26-5O is
13.8kcal/mol more stable than A16-5O.
During the third DA reaction, R26-5formation needs activation energy of 23.2 kcal/mol
(TS26-5O), which is nearly 3.0
kcal/mol less than its former step, but 5.2 kcal/molhigher than its
corresponding 6-6 analogue. The adduct,
A36-5 placed at -35.8 kcal/mol on PES,
gives rise to tetra-functionalized product,
P46-5 via a six-member transition
state, TS36-5of activation barrier
23.5 kcal/mol..The thermodynamic feasibility of
successive butadiene attachment to 16-5 is clearly
evident from the negative enthalpy values associated with all three
steps of the 6-5 MDA reaction. Moreover, the net energy release for the
overall reaction procedure is calculated to be -48.9 kcal/mol.
Similar to its 6-6 analogue, the addition of a second diene molecule to
the 6-5 bond of fullerene surface is observed to be a synchronous
process. Nevertheless, unlike the 6-6 one, the asynchronicity arises in
the case of third and fourth DA reactions as the difference of lengths
between the two newly formed C-C bonds in the TS is nearly 0.4 Å
(Figure S1 ).