Effect of external electric field on C-X ··· π halogen bonds.

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.

Quantum chemical computational studies on 5-(4-bromophenylamino)-2-methylsulfanylmethyl-2H-1,2,3-triazol-4-carboxylic acid ethyl ester.

The optimized molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) (1)H and (13)C 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 (1)H chemical shift values of the title compound in vacuum and in CHCl(3) 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.

Product operator descriptions of INEPT and RINEPT NMR spectroscopies for ISn (I=1/2, S=3/2) spin systems.

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 containing the 119Sn (I=1/2) and 35Cl (S=3/2) nuclei at the coupling constant of J(Sn-Cl)=375 Hz by using the Maple programme on computer.