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The geometries of triafulvene (TF) and its exocyclic Si, Ge, and Sn analogues complexes with F, Cl, Br, and I halogen atoms (TF(X)···Y, X═C, Si, Ge, and Sn; Y═F, Cl, Br, and I) were studied. The complexes were optimized at DFT(B3LYP)/6–311+G(d,p) level of theory. To assess the aromaticity of the considered complexes the geometry-based (HOMA), magnetism-based (NICS), and recently introduced electronic-based (electric field gradient (EFG(0); Shannon aromaticity (SA)) aromaticity indices were employed. The increasing tendency of aromaticity in each complex species was noted as the series of TF(X)···F > TF(X)···Cl > TF(X)···Br > TF((X)···I. Then, the binding energies corrected by basis set super position error (BSSE) were calculated by single point energy calculations at M06-2X/6-311+G(d,p) level. Natural bond orbital (NBO) analysis confirmed that the charge transfer takes place from TF(X) to the halogen atoms. Some topological parameters, within the framework of the quantum theory of atoms in molecules (QTAIM), were also calculated to estimate the aromaticity of the complexes. It was seen that there are some important correlations between the topological parameters and aromaticity indices. In addition the most striking finding was that all the TF(X) molecules are connected with the halogen atoms through Y···C1═C2 (π) noncovalent interaction. This interaction was also investigated through noncovalent interaction (NCI) analysis. [ABSTRACT FROM AUTHOR]

In this work, the aromaticity of polycyclic benzene rings was evaluated by the calculation of g -factor for a hydrogen placed perpendicularly at geometrical center of related ring plane at a distance of 1.2 Å. The results have compared with the other commonly used aromatic indices, such as HOMA, NICSs, PDI, FLU, MCI, CTED and, generally been found to be in agreement with them. So, it was proposed that the calculation of the average g -factor as Δ g could be applied to study the aromaticity of polycyclic benzene rings without any restriction in the number of benzene rings as a new magnetic-based aromaticity index. [ABSTRACT FROM AUTHOR]

In this work, the corrected total electron density [ABSTRACT FROM AUTHOR]

Geometric structures for all the possible isomers of fluorinated pyridines were optimized at the B3LYP/6-311++G(d,p) level of theory. Aromaticities of the considered molecules were investigated using different indices included geometry-based (HOMA and Bird [ I]), magnetism-based (NICS(1) and diamagnetic susceptibility anisotropy [Δχ]), π- and σ-electron count-based (pEDA, sEDA), and recently introduced electronic-based (electric field gradient [EFG(0), EFG(0.5)] and Shannon aromaticity) indices. Moreover, we used also HOMO-LUMO gap, atomization energy ( D), and interaction energy for fluorinated pyridine complexes by water molecule as global descriptors, and the EFG values (EFG(0)) on the middle points of C-F bonds and σ-electron population ( N) of nitrogen atom as local descriptors. All studied indices except HOMA and EFG(0.5) are well correlated to each other and to global and local descriptors. [ABSTRACT FROM AUTHOR]

Abstract: The optimized molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) 1H and 13C NMR shift values of 5-(4-bromophenylamino)-2-methylsulfanylmethyl-2H-1,2,3-triazol-4-carboxylic acid ethyl ester have been calculated by using Hartree–Fock (HF) and density functional method (DFT/B3LYP) with 6-31G(d), 6-31G(d,p) and LANL2DZ basis sets. The optimized molecular geometric parameters were presented and compared with the data obtained from X-ray diffraction. In order to fit the calculated harmonic wavenumbers to the experimentally observed ones, scaled quantum mechanics force field (SQM FF) methodology was proceeded. Correlation factors between the experimental and calculated 1H chemical shift values of the title compound in vacuum and in CHCl3 solution by using the conductor-like screening continuum solvation model (COSMO) were reported. The calculated results showed that the optimized geometry well reproduces the crystal structure. The theoretical vibrational frequencies and chemical shifts are in very good agreement with the experimental data. In solvent media the energetic behavior of the title compound was also examined by using the B3LYP method with the 6-31G(d) basis set, applying the COSMO model. The obtained results indicated that the total energy of the title compound decreases with increasing polarity of the solvent. Furthermore, molecular electrostatic potential (MEP), natural bond orbital (NBO) and frontier molecular orbitals (FMOs) of the title compound were performed by the B3LYP/LANL2DZ method, and also thermodynamic parameters for the title compound were calculated at all the HF and B3LYP levels. [Copyright &y& Elsevier]

The product operator descriptions of INEPT and reverse INEPT (RINEPT) NMR experiments are introduced for weakly coupled ISn (I=1/2, S=3/2 with n=1,2,3) spin systems. Explicit expressions for polarization transfer from spin-3/2 quadrupolar nuclei to spin-1/2 nuclei (and reversed polarization transfer) are given in detail by using the evolutions of product operators under the spin–spin coupling Hamiltonian. The results calculated for the intensities and positions of the observable signals are simulated in the molecules containning the 119Sn (I=1/2) and 35Cl (S=3/2) nuclei at the coupling constant of JSn–Cl=375 Hz by using the Maple programme on computer. [Copyright &y& Elsevier]

In this study, ab initio calculations (RI-MP2(full)/aug-cc-pVDZ) are performed to investigate the effect of an external electric field (EEF) on the nature, properties, and structures of C–X ··· π halogen bonds in CF3Br complexes with π systems (benzene, ethene, and ethyne), for the first time. This EEF effect is analyzed by a myriad of methods, including molecular electrostatic potential (MEP), symmetry adapted perturbation theory (SAPT), natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), and noncovalent interaction (NCI) methods. A linear relationship is found between RI-MP2 interaction energy and the strength of the EEF, indicating that the stability of C–X ··· π halogen bonds is sensitive to both the strength and direction of the EEF. According to the SAPT analyses, when the EEF is applied along the +z direction (perpendicular to the π plane), the nature of C–X ··· π halogen bonds transforms gradually from dispersion to electrostatic for the CF3Br ··· benzene complex and from electrostatic to more electrostatic for the other complexes. However, when the EEF is applied along the –z direction, the C–X ··· π halogen bonds in all the complexes tend to be more dispersive in nature. The QTAIM analysis exhibits that the CF3Br ··· benzene complex under the EEF with strength < 0.005 au is formed by the C–X ··· πC3 and C–X ··· πring halogen bonds, while it has only the C–X ··· πC3 halogen bond when the strength of the EEF is > 0.005 au. The structural results of the studied complexes show an inverse dependence of intermolecular distance between the CF3Br and π system on the strength of the EEF. [ABSTRACT FROM AUTHOR]