Kouichi Fukui

IRC approach to chemical dynamics: toward mode-selective chemical reactions

Abstract Ab initio MO calculations are presented on the asymptotic behavior of the intrinsic reaction coordinate (IRC), starting from the transition states of isomerization and fragmentation of formaldehyde in the vicinity of the equilibrium points of the reactant.

Ab initio MO calculations on the electronics structures of H2S+ and H2O+

Abstract Ab initio MO calculations for the potential curves of H2S+ and H2O+ are carried out in order to obtain a theoretical description of the electronic structure and geometry of these systems. The results are in satisfactory agreement with experiment and show that both radicals are very similar both in geometry and in electronic structure.

Detection of vanadyl-nitrogen interaction in organs of the vanadyl-treated rat: electron spin echo envelope modulation study.

ESEEM spectroscopy was applied for the first time to organs of an animal, viz. the kidney and liver of the rat treated with vanadyl sulfate. The aim of this study is to investigate the in vivo coordination structure of vanadyl ions administrated, and to gain information concerning the insulin‐mimic activity of vanadium. ESEEM measurements for kidney and liver performed at 77 K have established nitrogen coordination to a certain percentage of vanadyl ion in the organs. The rotios of nitrogen‐coordinating vanadyl ion were estimated as 70–80% in the liver, and 50–55% in the kidney. Isotropic portions of the 14N HFC were estimated as |A iso| ∼ 5.0 MHz for liver, and ∼ 5.2 MHz for kidney, indicating that the coordinating nitrogen is an amino nitrogen. Coordination of the Lys ϵ‐amine or the N‐terminal α‐amine of a protein or (a peptide) to vanadyl ion in vivo is suggested.

A hydrogen rearrangement of formamidine and the solvent effects thereupon

The nature of the 1,3 hydrogen rearrangement of formamidine (H2N-CH=NH) and the solvent effects on that reaction are studied with ab initio molecular orbital calculations on the basis of the supermolecule model. The reaction path and the motion of the migrating hydrogen atom are traced by using the concept of the intrinsic reaction coordinate (IRC). Four types of orientation of one water molecule to formamidine at the transition state of reaction are examined and the results are discussed from the standpoint of the orbital interactions.

MO CALCULATIONS OF EPISULFONIUM ION INTERMEDIATES AND REGIOSPECIFICITY IN THE ADDITIONS OF CL(

Abstract The calculations were carried out for the ethylene, propylene, iso-butylene and butadiene episulfonium ion intermediates by CNDO/2 method to optimize the geometric parameters and investigate the electronic states of the intermediates, resulting that the p-form intermediates were unexpectedly most stable. It was shown that the differences in extension of the lowest unoccupied molecular orbitals on ethylenic carbon atoms in the intermediates have an important role on the regiospecificity of the ring-opening additions of Cl− to the intermediates.

Effects of CoS torsion angle variation in a cobalt(II)-thiolate complex: X-ray crystal structure analysis, single-crystal EPR measurements and ligand-field calculations

Abstract X-ray structural determination and single-crystal EPR measurements were performed for (Me 4 N) 2 [Co(SPh) 4 ]. The compound crystallizes in the tetragonal space group P4 1 2 1 2 with a = 10.220(6), c = 32.316(16) A and Z = 4 . It was found that the Co(SPh) 4 2− anion has an approximate S 4 geometry: the four S′CoSC torsion angles are nearly the same (the mean value is 57.2°), where the S′CoS angle is bisected by the approximate S 4 axis, and the CoSPh units are almost planar. Analysis of the single-crystal EPR results provides effective g values of g ′ x = 2.34, g ′ y = 5.68 and g ′ z = 1.64. The g ′ z axis is most likely parallel to the approximate S 4 axis, and such a g ′ z axis direction was found to be consistent with the single-crystal EPR results. The g ′ values correspond to E/D = 0.30 and g ‖ = 2.09, g ⊥ = 2. in the S = 3 2 spin Hamiltonian description. These spin Hamiltonian parameters are contrasted with those of the D 2 d conformation anion in (Ph 4 P) 2 [Co(SPh) 4 ], which demonstrates the striking effects of the variation of the CoS torsion angles. Ligand-field calculations based on the angular overlap model were made with the aim of understanding the effects of torsion angle variation. It is shown that the striking torsion angle dependence can be understood in terms of the torsion angle dependent nature of the directions of CoS π and off-axis σ interactions. The calculations semi-quantitatively reproduce the contrasted magnetic properties of the two compounds.

On the interchain interaction in the (SN)x polymer

Abstract The interchain interactions in the (SN)x polymer are discussed on the basis of one-dimensional tight-binding SCF MO calculations of two chains of (SN)x. We conclude that the interchain interaction in the (100) crystallographic plane is more significant than that in the ( 1 02) plane in accordance with the previous result by Messmer and Salahub and that, from more quantitative analysis, these interactions are mainly caused by the shortest interchain SS coupling in both planes.

A theoretical study on the stability of the C3NN radical and its decomposition path

Abstract Ab initio SCF calculations have been carried out on the structure and stability of the CH 3 NN radical and its decomposition path. The participation of the vibrational structure of the radical in its stability and fragmentation are stressed. The results are compared with those for the CH 3 CO radical.

The relation between zero-field splittings and distortions along the normal coordinates in transition metal complexes

A systematic approach is developed for the ZFS (zero-field splitting) parameters D and E in slightly distorted tetrahedral and octahedral complexes with spatially non-degenerate ground states. This approach is illustrated by treatment of the normal coordinate system. The ZFS part of a spin Hamiltonian is expressed in terms of the distortion along normal coordinates and the coefficients characteristic of a metal-ligand combination. This expression for a spin Hamiltonian clarifies the relation between the ZFS and the distortions of the coordination geometry from Td and Oh symmetries, and is particularly useful in the calculation of the ZFS under non-axial distortions. Some of the coefficients are derived for the ground A2 state (tetrahedral d7 and octahedral d3) ions in terms of the e σ and e π parameters of the angular overlap model. Satisfactory agreement is obtained in the application of the approach to Cs3CoCl5, Cs2CoCl4 and ruby.

Magnetic properties of a penta-coordinated high-spin cobalt(II) complex: acetate-N-methyl-octaethylporphyrinato-cobalt(II)

It is shown by EPR and magnetic susceptibility (χ) measurements that acetate-N-methyl-octaethylporphyrinato-Co(II) has a high-spin ground state. The complex in toluene gives EPR spectra with g= 4.4 and 2.04 and χ with μeff= 4.4 BM and D ≈ 20 cm−1, which indicates square-pyramidal geometry around Co (II). Data for the undiluted system are analyzed in terms of a dimer model with a small exchange interaction.