THE EVALUATION OF PROTONATION ENERGY OF MOLECULES IN TERMS OF QUANTUM THEORETICAL DESCRIPTORS - Theoretical and Computational Research in the 21st Century - page 217

10.8 PRESENT MODEL REGARDING PROTONATION

In this work, we have developed a model for the evaluation of PA in terms
of some akin conceptual reactivity descriptors that can be conceptually
linked and associated with the physicochemical process of protonation.
The akin descriptors are the ionization energy (I), the global softness (S),
the electronegativity (χ), and the global electrophilicity index (ω).

THE MODELING OF THE PHYSICOCHEMICAL PROCESS OF
PROTONATION AND ALGORITHM FOR COMPUTING THE
PROTON AFFINITY OF THE MOLECULES

The descriptors such as the ionization process of atoms and molecules, the
physical property such as hardness, softness, the electronegativity, and the
electrophilicity have close relation, that is, akin with each other in their
operational significance and origin.
We have tried to posit above that the physicochemical process of pro-
tonation can be linked to the above akin descriptors: the ionization process,
the hardness, softness, electronegativity, and electrophilicity. Recently,
Ghosh et al. [80-88] have published good number of papers where they
[80-88] have discussed that the three descriptors, the electronegativity, the
hardness, and the electrophilicity index of atoms and molecules are fun-
damentally qualitative per se and operationally the same. All these three
descriptors represent the attraction of screened nuclei toward the electron
pair/bond. Thus, we can safely and reasonably conclude that the PA and
the three descriptors have inverse relationship.
Thus, since the above four parameters have dimension of energy and
can be linked to the process of charge rearrangement and polarization dur-
ing the physicochemical process of protonation, they can be components
of a probabilistic scientifi c modeling of PA. The physicochemical process
of protonation has direct link to the charge polarization and alteration of
electron distribution in the molecule.
The PA or the ability of donating the lone pair of a Lewis base and the
ability for the deformation of electron cloud of a species, the softness, and/
or the tendency of the molecule to lose electron, the ionization potential,
are fundamentally similar in physical appearance stemming from the at-
traction power of the nuclei of the atoms forming the molecule. The soft-
ness, the ionization energy, the electronegativity (chemical potential), and