Acids and bases
In Klopman's(and Salem's) equation,
the second term is the Coulomb term and the third term is the electron transfer interaction term.
The reaction between a strong acid and a strong base can be explained and interpreted by the second term,
and the reaction between a weak acid and a weak base can be explained and predicted by the third term.
The coupling reaction between a weak acid and a weak base
When a covalent bond is formed due to the reaction of a weak acid and a weak base,
that reaction is a type of the coupling reaction.
Therefore, the coupling reaction is explained by the control of electron transfer interaction.
Electrostatically (+) is LUMO and electrostatically (-) is HOMO,
but the signs of molecular orbitals are (+) and (+) or (-) and (-).
This reaction is useally symmetrical acceptable.
The closer difference in energy level between LUMO and HOMO and the larger molecular orbital coefficients of their reaction atoms make the larger electron transfer interaction.
⊿Etotal=ーqr・qs ／ Rrs ＋2(Cmｒr・ Cnｓs・⊿β)² ／(E*nrーE*ms)
(the second term) (the third term) (the first term is omitted)
(coulomb term) (electron transfer interaction term)
where
E*nr is the energy level of the coupler anion's HOMO,
E*ms is the energy level of quinonediimine's LUMO,
Cmrr is the molecular orbital coefficient of carbon atom on the coupler's(HOMO's) active point ,
Cnss is the molecular orbital coefficient of nitrogen atom on the quinonediimine's(LUMO's) reaction point ,
Δβ is the stabilization energy due to the formation of CN bond.
It's equivalent to the amount of change in the resonance integral.
