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Perturbed Hartree-Fock calculations are performed on the molecules CH4, C2H2, C2H4, C2H6, CH3F, CH3OH, H2O, NH3, and C6H6 to obtain the heavy-atom NMR shielding constants and magnetic susceptibilities. Slater-type atomic orbitals (STO's) are used as the basis set. Various aspects of this model, including the dependence on basis-set size and on the origin of the vector potential, are examined. The results are compared with the available experimental data and with other ab initio and semiempirical treatments.

of the solvent, the residue was recrystallized from chloroformethanol, white needles, mp 239°(lit.27 239-240°), 92% after recrystallization. The uv absorption spectrum agreed with that published for DPP.9Techniques and apparatus used for voltammetry and coulometry have previously been described.11.28 TFA was reagent grade and used without further purification. Reagent grade dichloromethane was passed through a column of neutral aluminum immediately before use. Reagent grade TPE was recrystallized before use.

The theoretical study of Flygare et al. on one-electron properties of the formaldehyde molecule is extended to include the paramagnetic susceptibility and the 13C and 17O NMR shielding constants and to investigate their sensitivity to Slater basis-set quality. The Gaussian transform method is used to evaluate the necessary integrals. Using the fully coupled perturbed Hartree-Fock formalism, we find that improvements in the wavefunction produce significant changes in most components of the second-order properties. The best shielding calculations, obtained with a double-zeta Slater set, are within the rather large experimental uncertainties, whereas the agreement between the theoretical and experimental susceptibility results is less satisfactory. The complete paramagnetic tensors are analyzed in terms of MO and AO contributions. Comparisons are made with other ab initio calculations and with simplified forms of the theory.

Articles you may be interested inThe dynamical behavior of a small probe molecule dissolved in a nematic liquid crystal studied by NMR J. Chem. Phys. 78, 1712 (1983; 10.1063/1.444956 19F shielding anisotropies of the fluoromethanes obtained from NMR studies in a smectic liquid crystal solution J. Chem. Phys. 66, 989 (1977); 10.1063/1.434010 Deuterium magnetic resonance study of a smectic liquid crystalThe fluorine-19 shielding anisotropies of CFJCI, CF 3 Br, CFJI, and CF J CCl 3 have been determined from analyses of fluorine NMR spectra in partially ordered smectic liquid crystal solutions. The high degree of orientation and increased solubility produced in the smectic phase leads to measurements of 0" II -0" 1 for each of these systems to relatively high accuracy. The anisotropies obtained for the trifluorohalomethanes are found to increase in the order: CF 3 Cl, -13.4±O.5 ppm; CFJBr, 2.7±O.3 ppm; CFJI, 16.8±O.2 ppm. The quantity 0"11 is approximately constant for each of the CF 3 X molecules studied. This feature permits an estimate of the shielding and spin-rotation constants of CF •.