Using a regioselectivity descriptor known as Fukui indices, this theoretical study examines the reactivity of cycloaddition processes of benzamide (PhCONH2) and chlorocarbonylsulfenyl chloride (ClCOSCl) at the level of base 6-311 G (d. p) by use of the DFT approach. Therefore, the attack of the sulfur atom on nitrogen and carbon on oxygen is kinetically more preferred than the assault of the sulfur atom on oxygen and carbon on nitrogen, as we have observed from our study. The electrophilic Δω difference between chlorocarbonylsulfenyl chloride and benzamide is 1.3726 eV. This indicates that the reaction under investigation has a polar nature (Δω > 1). on oxygen and carbon on nitrogen, as we have observed from our study. We have also studied the stereoselectivity and feasibility of these reactions from a thermodynamic and orbital point of view. The transition states of this reaction have been determined.

Oxadiazoles, a class of nitrogen-containing heterocycles, exhibit diverse applications in pharmaceuticals, industry, and other fields. This study employs Density Functional Theory (DFT) to investigate the structural, electronic, and spectroscopic properties of four oxadiazole isomers. The B3LYP functional and the 6-311G(d,p) basis set were used for calculations. Frontier orbital energies, energy gap, chemical reactivity descriptors, dipole moment, and thermodynamic properties were computed. Additionally, IR and UV spectra were analyzed. The results indicate significant variations in electronic and thermodynamic properties among the isomers. Isomer 4 demonstrated the highest stability and electrophilicity. The calculated IR and UV spectra were compared with available experimental and theoretical data. The study provides valuable insights into the structural and reactivity trends within the oxadiazole family, contributing to a deeper understanding of their potential applications.

In this work, two organic materials as dyes, namely, methylene blue (MB) and methyl red (MR), have been proposed to play the role of the electron donor in organic photovoltaic (OPV) cells. We use the PCBM as a well-known electron acceptor. The density functional theory (DFT) method has been used to determine the electrostatic potential and the frontier molecular orbitals (FMO), of the methylene blue (MB) and the methyl red (MR) compounds. Nonlinear optical (NLO) descriptors have been determined for the two compounds. The potential energy surface analysis has been performed by the DFT method using the exchange and correlation of Becke, Lee, Yang, and Parr Gradient Corrected Functional (B3LYP) with the standard 6-31G(d) base. We have performed another theoretical study using quantum time-dependent density functional theory (TD-DFT) on both MB and MR as organic dyes to determine their UV-Vis spectra. The results of the energy gap, chemical hardness, dipole moment, and hyperpolarizability show that MB may be chemically more reactive Than MR. The present work has proposed a bilayer organic photovoltaic (OPV) cell to contribute to the valorization of the two dyes as solar materials. The developed photovoltaic cell project has used electrical and energetic parameters that can describe the OPV cell based on ([MB or MR]: PCBM). Open-circuit voltage (Voc), excitation energy, and oscillator strength have been theoretically determined. The results of the present work showed a remarkably high open circuit voltage, especially in the case of methyl red (1.55 V) more than in the case of the methylene blue (0.84 V) so that both of the two dyes can be a good candidate for organic solar cells.

The FTIR and Raman spectra of dopamine were also recorded in the spectral region 20 - 4000 cm^-1 and 400 - 4000 cm^-1 respectively. The optimized molecular geometry and fundamental vibration frequencies are interpreted using structural optimizations based on the DFT method. The B3LYP / 6-311G (d, p) was used to determine the calculations of the chemical descriptor. The dopamine (DA) molecule can acquire a maximum charge of 0.513 eV from its environment. To understand the molecular interactions of Dopamine, the MEP is a crucial tool. Nonlinear optical descriptors (NLO) and the lengths, bond angles are also determined by DFT and MP2 methods. The DFT method was used to determine the chemical shifts of ¹H and ¹³C of the product. These constants have been calculated by employing the GIAO (Gauge-Including-Atomic-Orbit), CSGT (Continuous Set of Gauge Transformations) and IGAIM (Individual Gauges for Atoms In Molecules) methods at the B3LYP/6-311G (d, p). The comparison of the theoretical chemical shifts with the experimental ones shows that the CSGT method is the best.

The FT-IR spectrum of salicylic acid (SA) was studied in the region 10-4000 cm-1. The optimized molecular geometry and fundamental vibration frequencies are interpreted using structural optimizations based on the Functional Density Theory (DFT) method. Additionally, we used B3LYP / 6-311G (d, p) to determine the chemical descriptor, the ionization potential (I), the electron affinity (A), the chemical potential (μ), the chemical hardness (η). Nonlinear optical descriptors (NLO) such as dipole moment (μ), polarizability (α), first hyperpolarizability (β) and second hyperpolarizability (γ), 3D maps of HOMO and LUMO orbitals, lengths and Bond angles of salicylic acid isomers are also determined by both DFT and MP2 (The Møller-Plesset theory of order 2 perturbation) methods. The overall descriptors and the non-linear optical properties confirmed that salicylic acid is the reactive molecule and para-hydroxybenzoic acid is the stable molecule. An electrostatic molecular potential (MEP) study was also performed to determine the reactivity of molecules.