Basis Electronic Activity of Molecular Systems. A Theory of Bond Reactivity

In this paper, we present a new finding, the basis electronic
activity
(BEA) of molecular systems; it corresponds to the significant, although
nonreactive, vibrationally induced electronic activity that takes
place in any molecular system. Although the molecule’s BEA
is composed of an equal number of local contributions as the vibrational
degrees of freedom, our results indicate that only stretching modes
contribute to it. To account for this electronic activity, a new descriptor,
the bond electronic flux (BEF), is introduced. The BEF combined with
the force constant of the potential well hosting the electronic activity
gives rise to the effective bond reactivity index (EBR), which turns
out to be the first density functional theory-based descriptor that
simultaneously accounts for structural and electronic effects. Besides
quantifying the bond reactivity, EBR provides a basis to compare the
reactivities of bonds inserted in different chemical environments
and paves the way for the exertion of selective control to enhance
or inhibit their reactivities. The new concepts formulated in this
paper and the associated computational tools are illustrated with
characterization of the BEA of a set of representative molecules.
In all cases, the BEFs follow the same linear pattern, whose slopes
indicate the intensity of the electronic activity and quantify the
reactivity of chemical bonds.