This study is focused
on describing the molecular mechanism beyond
the molecular picture provided by the evolution of molecular orbitals,
valence bond structures along the reaction progress, or conceptual
density functional theory. Using bonding evolution theory (BET) analysis,
we have deciphered the mechanism of the 1,3-dipolar rearrangement
between acetonitrile oxide and (1
S
,2
R
,4
S
)-2-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yl acetate
derivatives. The BET study revealed that the formation of the C–C
bond takes place
via
a usual sharing model before
the O–C one that is also formed in the halogenated species
through a not very usual sharing model. The mechanism includes depopulation
of the electron density at the N–C triple bond and creation
of the V(N) and V(C) monosynaptic basins, depopulation of the former
C–C double bond with the creation of V(C,C) basins, and final
formation of the V(O,C) basin associated with the O–C bond.
The topological changes along the reaction pathway take place in a
highly synchronous way. BET provides a convenient quantitative method
for deriving curly arrows and electron flow representation to unravel
molecular mechanisms.
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