THE EVALUATION OF PROTONATION ENERGY OF MOLECULES IN TERMS OF QUANTUM THEORETICAL DESCRIPTORS - Theoretical and Computational Research in the 21st Century - page 228

reveals that there are excellent correlation between the theoretically com-
puted PAs of the seven hydrocarbons (Set 1), seven aliphatic amines (Set
3), and 40 pyridine derivatives (Set 5), respectively. The R 2 value for cor-
relation of Set 1, Set 3, and Set 5 are 0.99, 0.995, and 0.911, respectively.
A close look at the Figures (10.1), (10.3), and (10.5) reveals that the two
sets of PAs—experimental and theoretical of the three sets molecules viz
the hydrocarbons (Set 1), the aliphatic amines (Set 3), and pyridine deriva-
tives (Set 5) are so close to each other that one curve just superimposes
upon the other.
A look at Table (10.3) and Figure (10.2) (for Set 2); Table (10.5) and
Figure (10.4) (for Set 4); and Table (10.7) and Figure (10.6) (for set 6) re-
veals that there is fairly a good correlation between the theoretically com-
puted and experimentally determined PAs of as many as 12 compounds
containing alcohols, carbonyls, carboxylic acids and esters (Set 2), 17
aromatic amines (Set 4), and 10 amino acids (Set 6), respectively. The R 2
value for correlation of Set 2, Set 4, and Set 6 are 0.817, 0.91, and 0.88,
respectively.
10.11 CONCLUSION
From the literature survey, it is understood that there is enough scope to
model to calculate the protonation energy, and we have presented a scien-
tific model for the evaluation of protonation energy of molecules in terms
of four quantum theoretical descriptors—the ionization energy, the global
softness, the electronegativity, and the global electrophilicity index. As
a basis of scientific modeling, we have posited that these akin theoreti-
cal descriptors can be entailed in following and describing the alteration
in geometrical parameters, the charge rearrangement, and polarization in
molecules as a result of protonation. The suggested ansatz is invoked to
calculate the PAs of as many as 93 carbon compounds of diverse physi-
cochemical nature. The validity test of the model is performed by com-
paring theoretically computed protonation energies and the corresponding
experimental counterparts. The close agreement between the theoretically
evaluated and experimentally determined PA's suggests that the conceived
modeling and the suggested ansatz for computing PA of molecules are ef-
ficacious and the hypothesis is scientifically acceptable.
In summary, it is clear that quantum chemical descriptors have tremen-
dous applicability and potential in the study of protonation phenomenon.