Sulfur Orbitals Research Articles

MO studies on the33S hyperfine splittings andg-factors of dithiin cation radicals

The spin distribution and g-factors have been calculated for a number of dithiin cation radicals. The s-spin densities on sulphur calculated by the open-shell unrestricted INDO method both with and without annihilation of the quartet component have been correlated satisfactorily with the observed 33S hyperfine splittings. The g-factors calculated according to the Stone theory by an open-shell restricted version of the INDO method are found in good agreement with observation; their deviation from the free-spin comes from the large spin density localized on the sulphur atoms and the small excitation energy from the ‘NB’ sulphur orbitals to the odd MO. Comparative calculations with the sp and spd basis sets demonstrate the modest effect of the 3d(S) orbitals on the considered physical constants of the dithiin cations.

Esr and structure of sulfur-centered radicals and radical ions. γ-Irradiated dimethyl disulfide and methane thiol single crystals at 77°k

Single crystals of dimethyl disulfide and methane thiol were irradiated at 77°K. CH 3S radicals were produced in both compounds and measurement of the isotropic coupling constant from the methyl protons gave a value of 7.6 G. In the dimethyl disulfide crystal both the anion, CH 3SSCH 3, and the cation, CH 3SSCH + 3, radicals were observed. The disulfide anion radical exhibited an isotropic septet of lines with a = 5.0 G. Comparison with measurements on a polycrystalline sample gave g⊥ = 2.020 and g‖ = 2.000 for this radical. The disulfide cation radical exhibited an evenly spaced septet of lines with a = 9.1 G and a maximum value for the g factor of 2.032. On illumination with IR radiation (λ > 590 mm) the disulfide cation radicals were easily bleached together with about 50% of the disulfide anion radicals suggesting a photoinduced neutralization process. The presence of weak 33S satellite lines in the anion radical spectrum indicates that 12% of the unpaired spin is localized to the two sulfur 3s orbitals. The structure of the disulfide cation radical is discussed in relation to earlier studies and a dihedral angle of 180° is proposed. The mechanisms for radical formation and decay in dimethyl disulfide and methane thiol are also discussed.

Optical Properties of a Magnetic Semiconductor: Chalcopyrite CuFeS. II. Calculated Electronic Structures of CuGaS2:Fe and CuFeS2

In order to study the electronic structures of CuGaS 2 : Fe and CuFeS 2 , the problem is simulated by large clusters of these crystals. The system is treated as a “large molecule” and the energies and wavefunctions for the molecule are obtained using a semiempirical molecular orbital method. The unoccupied molecular orbitals originating from iron 3d orbitals in CuGaS 2 : Fe are well localized on the iron ion, while the corresponding orbitals in CuFeS 2 have a considerable admixture of sulfur 3p orbitals. The molecular orbitals corresponding to uppermost states of the valence band are composed of sulfur 3p and copper 3d orbitals. It is derived from the comparison between the observed and calculated absorption spectra that the A and B absorption bands in CuGaS 2 :Fe arise from the charge transfer transitions from the valence band to the unoccupied states originating from the iron 3d orbitals and the absorption band edge in CuFeS 2 arises from the corresponding transitions.

ChemInform Abstract: ROLE OF SULFUR D ORBITALS IN ISOTHIOCYANIC ACID AND AN ELECTRONIC‐STRUCTURE COMPARISON WITH ISOCYANIC ACID

The electronic structure of isothiocyanic acid, HNCS, was determined by an ab initio LCAO‐MO‐SCF calculation. Isocyanic acid, HNCO, was also calculated and the two molecules are compared. The basis set consisted of uncontracted, atom‐optimized Gaussian functions, with nine s plus five p exponents to describe the sulfur and five s plus two p apiece for the carbon, nitrogen, and oxygen. The hydrogen was represented by three s‐type functions. An additional calculation of HNCS was carried out by adding a d set to the description of the sulfur. The molecular orbitals of HNCS are analyzed using simple perturbation theory applied to the localized valence‐bond functions and the SCF orbitals are displayed using planar electron‐density plots. The electronic structure of HNCS is compared with that of HNCO and it is concluded that (1) the π system in HNCS involves a nitrogen lone pair stabilized by a higher‐lying C–S π bond while the π system of HNCO consists of a C–O π bond stabilized by the higher‐energy nitrogen lone pair and (2) the d orbitals of sulfur are accepting density in a σ rather than a π fashion.

Role of sulfur d orbitals in isothiocyanic acid and an electronic-structure comparison with isocyanic acid

The electronic structure of isothiocyanic acid, HNCS, was determined by an ab initio LCAO-MO-SCF calculation. Isocyanic acid, HNCO, was also calculated and the two molecules are compared. The basis set consisted of uncontracted, atom-optimized Gaussian functions, with nine s plus five p exponents to describe the sulfur and five s plus two p apiece for the carbon, nitrogen, and oxygen. The hydrogen was represented by three s-type functions. An additional calculation of HNCS was carried out by adding a d set to the description of the sulfur. The molecular orbitals of HNCS are analyzed using simple perturbation theory applied to the localized valence-bond functions and the SCF orbitals are displayed using planar electron-density plots. The electronic structure of HNCS is compared with that of HNCO and it is concluded that (1) the π system in HNCS involves a nitrogen lone pair stabilized by a higher-lying C–S π bond while the π system of HNCO consists of a C–O π bond stabilized by the higher-energy nitrogen lone pair and (2) the d orbitals of sulfur are accepting density in a σ rather than a π fashion.

The 3d orbitals of phosphorus and sulfur

The 3d orbitals of phosphorus and sulfur

Deuteroexchange study of 3d orbital conjugation in organic sulfides

The kinetics of dedeuteration under the action of potassium amide in liquid ammonia in a series of sulfides with open chain, open chain-alicyclic and open chain-aromatic substituents and a number of their oxygen analogs have been determined to investigate the electronic effect of 3d orbital conjugation in divalent sulfur compounds. The conjugation of the 3d orbitals of sulfur has been studied (1) with the adjacent, negatively charged carbon electrons of the intermediate carbanion; (2) with a pair of unshared electrons of the substituent (OMe, N(Me 2); via the benzene ring) in the ground state of the sulfide molecule; (3) with the charge ( via the benzene ring) in the intermediate anion formed in the exchange reaction. (4) In addition hyperconjugation of the type - S CH 2H + has been investigated.

A unique sulfur ylide reaction: on the question of R 4S intermediates

The question of the availability of the sulfur Td orbitals for bonding 3 in the ground state remains unanswered despite many studies. In the case where the ligands are carbon, two types of such systems must be considered. Type A possesses three sigma and one pi bond to sulfur as represented by the ylides; whereas, type B possesses four sigma bonds to sulfur. Intermediates 88 R.$-CHe e R2:=CH2 R4S: Type A Type B

Electronic Spectra and Structure of Sulfur Compounds

The lower-energy electronic states of a series of saturated sulfur compounds have been investigated theoretically and experimentally. The compounds investigated fell into two categories: the monosulfide series ABS in which the substituents A and B were varied, and the polysulfide series R2Sn, where n=1, 2, 3, and 4 and where R was usually CH3. The data collected included ultraviolet vapor spectra, solution spectra, solvent shifts, and vibrational data. Computations followed an approach related to that of Wolfsberg and Helmholz. This theoretical method closely approximates the experimentally observed energies in the compounds containing a single sulfur atom but encounters difficulties when two or more sulfurs are present because of the large 3dS−3dS and 4sS−4sS interactions which are predicted. It is indicated that the lower-energy excited electronic states of all the monosulfide compounds investigated are of a molecular nature in which the 4sS and 3dS atomic orbitals of sulfur play particularly dominant but by no means exclusive roles. The lower-energy excited states of the molecules R2Sn, n=2, 3, and 4, also contain significant 4s and 3d character; additionally, however, they are of S–S antibonding nature.

D Orbitals in Compounds of Second-Row Elements. I. SF6

Optimum exponent values for 3s, 3p, and 3d orbitals of sulfur in SF6 have been calculated in an electrostatic approximation. The sulfur electrons are perturbed by fluorine potentials appropriate to self-consistent field wave functions for the fluorine orbitals, and the energy minimized with respect to wave-function exponents. The optimum values are k3s=2.0, k3p=1.6, and k3d=1.2, corresponding to expansion of 3s and 3p orbitals, and contraction of 3d, compared with free-atom values. The values are remarkably stable to changes in valence-orbital configurations as between SF6, S+F6−, S++F6=, and even S−F6+. They are also little affected by change in hybridization at fluorine, and should therefore be suitable for use in the construction of molecular wave functions. Although the calculated energies include no exchange terms they are still of some interest. They suggest for example that the promotion energy to the configuration sp3d2 of sulfur (estimated to be 25–31 eV) can be compensated by the energy of molecule formation.