Proton transfer from 1,4-pentadiene to superoxide radical anion: a QTAIM analysis

We studied the bis-allylic proton transfer
reaction from 1,4-pentadiene to superoxide
radical anion (O2
·־). Minima and
transition state geometries, as well as
thermochemical parameters were computed
at the B3LYP/6-311+G(3df,2p)
level of theory. The electronic wave
functions of reactants, intermediates,
and products were analyzed within the
framework of the Quantum Theory of
Atoms in Molecules. The results show
the formation of strongly hydrogen bonded
complexes between the 1,4-pentadien-
3-yl anion and the hydroperoxyl
radical as the reaction products. These
product complexes (PCs) are more stable
than the isolated reactants and much
more stable than the isolated products.
This reaction occurs via pre-reactive
complexes which are more stable than
the PCs and the transition states. This is
in agreement with the fact that the net
proton transfer reaction that leads to free
products is an endothermic and nonspontaneous
process.