Compounds 1 and 2 were subjected to DFT measurements. Figures 11 and 12 depicts optimized molecular structures of the most stable types. Table 3 shows the measured and relative energies of the participants. Theoretical findings using the measurement method proposed in this study revealed that compound 2 is more stable than other compounds based on the following factors: total energy, and higher energy orbital molecular occupied (EHOMO), Calculations of molecular orbitals provide a comprehensive overview including their spatial properties, of orbitals. Private atom contributions and nodal trends The contour plots of the frontier orbitals for ground states 1 and 2 are shown in Figs. 12 and 13, including “the Highest Occupied Molecular Orbital” (HOMO) and “the Lowest Unoccupied Molecular Orbital” (LUMO).
It's worth noting how equally both orbitals are distributed around the conjugation plane. Figures 3&4 show that the substituted molecule has HOMO orbitals, whilst the LUMO orbitals are identical to those of the unsubstituted molecule, meaning that the substitution affects the electron donation potential. The ability to accept electrons, on the other hand, is just slightly harmed. Table 3 Compounds 1 and 2's the orbital energy levels of HOMO and LUMO are stated. The disparities in energy between HOMO and LUMO are approximately 4.0099, 2.2507ev. In the case of compound 1, and 2, respectively. Compound 2 also describes the lower the HOMO, LUMO, and energy gap values are, the better. which describes the reaction of final shipping transport within the molecules.
3.6.2 Geometrical optimization
In order to understand the molecular properties of the synthesized compounds (1) and (2), we carried out their structural optimization and the energies of the Highly Occupied Molecular Orbital (HOMO) and Least Unoccupied Molecular Orbital (LUMO) were evaluated from the optimized structures. Further, the energies of HOMO and LUMO were utilized to calculate some of the parameters like electronegativity (χ), chemical potential (α), hardness (η), electrophilicity index (ω), electron affinity (I) and ionization potential (A) to understand the reactivity of the studied molecules. The global parameters have been calculated by using the following equations.
Ionization potential (I) is related to the energy of the EHOMO through the equation [21]:
I = -EHOMO ……..(2)
Electron affinity (A) is [21] related to ELUMO through the equation:
A = -ELUMO ……..(3)
When the values of I and A are known, one can determine the electronegativity χ and the global hardness (η).
The electronegativity [22], can be estimated by using the equation:
χ = \(\frac{I+A}{2}\)...........(4)
Chemical hardness (η) measures the resistance of an atom to charge transfer [22], it is estimated by using the equation:
η = \(\frac{I-A}{2}\)...........(5)
Chemical softness (S), the reverse of hardness [22], is estimated by using the equation:
S = \(\frac{1}{\eta }\) ………(6)
electrophilicity index(ω) as follows.
ω = \(\frac{ {\mu }^{2} }{2\eta }\)………..(7)
Where µ is the electronic chemical potential [23]:
µ = - χ .............(8)
The calculated HOMO-LUMO energies and global parameters of the synthesis compounds (1) and (2) are displayed in Table 3.
The tabulated data reveals that, low energy gap, chemical hardness and electrophilicity index values are responsible for the good biological activity of the pyridine derivative (2) [24, 25].
The optimized molecular structures and HOMO-LUMO energy level diagrams of the synthesis compounds (1) and (2) were shown in Figs. 11, 12, 13, and 14 and Table 4. The reactivity of molecules often decided by using density functional theory (DFT) and that is based on the energy differences between the HOMO and LUMO. From the literature review, it was observed that if the difference between the HOMO and LUMO is small, the energy required to excite an electron to higher energy state is less and therefore the molecules become more reactive chemically and biologically [26, 27].
Table 4
The quantum chemical parameters evaluated for the synthesis compounds (1) and (2) by DFT method at B3YLP/6-31G (d, p).
Electronic parameters
|
(1)
|
(2)
|
Electronegativity (χ)
|
4.645
|
3.951
|
Electron Chemical potential(µ)
|
-4.645
|
-3.951
|
Chemical Hardness(η)
|
2.004
|
1.125
|
Chemical softness (S)
|
0.215
|
0.253
|
Electrophilicity index (ω)
|
5.383
|
6.937
|
Ionization potential (I)
|
6.650
|
5.077
|
Electron affinity (A)
|
2.640
|
2.826
|
If the gap is large, then the promotion of electron becomes difficult and requires lot of energy, so that the molecules become more stable towards any reaction. Thus, from the above discussion it is inferred that the theoretical modeling is most useful in the interpretation of chemical reactivity, kinetic stability, polarizability and biological properties of the molecules [28, 29].