The performance of different DFT ~UDFT-IGLO, UDFT-GIAO, SOS-DFPT-IGLO! and hybrid-DFT approaches, as well as of HF-GIAO and MP2-GIAO methods has been compared for the calculation of O chemical shielding in the series of tetrahedral d oxo complexes MO4~M5Fe,Ru,Os!, MO4 ~M5Mn,Tc,Re!, and MO4 ~M5Cr,Mo,W!. While HF-GIAO and MP2-GIAO fail for systems with low-lying excited states ~e.g., MnO4 , CrO4 ...

The molecular structure of 1-selena-closo-dodecaborane(11), 1-SeB11H11, has been determined by the concerted use of quantum chemical calculations and gas-phase electron diffraction. The structure has C(5v) symmetry and is distorted from a regular icosahedron mainly through the expansion of the pentagon of boron atoms adjacent to selenium, with r(a3,1)(B-B) = 192.2(2) pm. The Se-B bond length is...

The molecular structure of closo-9,12-(SH)2-1,2-C2B10H10 has been determined by the concerted use of quantum chemical calculations and gas electron diffraction (GED). For the purposes of GED, the architecture of the carbaborane cage was simplified to allow it to have C2v symmetry, while the positioning of the thiol groups means that the molecule had overall C1 symmetry. The accuracy of the expe...

The long-held “shielding cone” model of the through-space NMR shielding effect of a carbon-carbon double bond predicts only the effect of the magnetic anisotropy of the double bond; it ignores other important contributors to the overall shielding. GIAO-SCF and GIAO-MP2 calculations have been performed on a simple model system, methane moved sequentially above ethene or 2-methylpropene. These ca...

The structures of a number of fluorocarbocations were calculated at the correlated MP2/6-31G* level. 13C and 19F NMR chemical shifts of fluorocarbocations were calculated for the first time using IGLO and GIAO-MP2 methods. The data showed good correlation of calculated 19F and 13C NMR chemical shifts with the experimental chemical shifts of fluorocarbocations. The correlation for GIAO-MP2-calcu...

Isotropic 13C chemical shifts of the ribose sugar in model RNA nucleosides are calculated using SCF and DFT-GIAO ab initio methods for different combinations of ribose sugar pucker, exocyclic torsion angle, and glycosidic torsion angle. Idealized conformations were obtained using structures that were fully optimized by ab initio DFT methods starting with averaged parameters from a collection of...

We present the gauge invariant atomic orbital ~GIAO! calculation of nuclear magnetic shieldings for solvated molecules described within the polarizable continuum model ~PCM!. The performance of the PCM-GIAO approach is tested in a benchmark calculation of isotropic C, N, and O shielding constants for CH3CN and CH3NO2 in vacuo and in water, both at the Hartree–Fock and density functional levels ...

Helium-3 NMR chemical shifts of various (3)He-encapsulated fullerenes ((3)He@C(n)()) and their derivatives have been calculated at the GIAO-B3LYP/3-21G and GIAO-HF/3-21G levels with AM1 and PM3 optimized structures. A good linear relationship between the computed (3)He NMR chemical shifts and the experimental data has been determined. Comparisons of the calculation methods of (3)He NMR chemical...

Pinus krempfii Lecomte (Pinaceae) is an endemic tree to Vietnam with restricted habitats at higher altitudes in the highlands. In this study, genetic variation of four populations of P. krempfii was assessed using 17 microsatellite markers (single sequence repeats). Of these 17 markers, eight were polymorphic, and among the 42 putative alleles amplified, 32 were polymorphic (accounting for 76.1...

A comparative study of the 2,3-dimethyl-3-fluoro-2-butyl cation and its chloro analog was carried out by the ab initio/GIAO-CCSD(T) (gauge invariant atomic orbital-coupled cluster with single, double, and perturbative triple excitation) method. The structures and (13)C NMR chemical shifts of the cations were calculated at the GIAO-CCSD(T)/tzp/dz//MP2/cc-pVTZ level. Bridged fluoronium ion 1, car...