Note on the electron–electron counterbalance hole

The electron–electron counterbalance hole implies that two parallel spin electrons cannot be at opposite positions with respect to the spatial inversion center, if it exists. The hole is known to appear for any approximate and exact wave functions with an even inversion parity. We point out that for particular cases, the counterbalance hole also appears when wave functions have an odd inversion parity and two electrons with anti-parallel spins are involved.     

Densities and Viscosities of Tris(acetylacetonato)cobalt(III) Complex Solutions in Various Solvents

The densities and the viscosities of tris(acetylacetonato)cobalt(III) solutions in acetonitrile, dichloromethane, chloroform, tetrachloromethane, benzene, toluene, ethylbenzene, and p-xylene were measured in the dilute concentration regions at several temperatures ranging from 278 to 313 K under ambient pressure. The partial molar volumes of the solvents and solute were calculated. They are independent of concentration and increase slightly as the temperature increases. The viscosity A- and B-coefficients of the Jones-Dole equation were obtained. The A-coefficients were found to be zero within experimental error. The B-coefficients are positive and decrease as the temperature increases. Thermodynamic quantities of activation for viscous flow were calculated on the basis of Eyring’s viscosity equation. From the quantities obtained in this study, along with some information from the literature, it is suggested that structure-making interactions occur between the segments of the complex and the solvent molecules. These interactions include electrostatic interactions between the local charge on the complex and the dipole moment of the solvent in solutions of acetonitrile and dichloromethane, interlocking packing interactions along C ₃-axis of the complex with solvent in solutions of chloroform and tetrachloromethane, and π-electron interactions between the chelate ring of the complex and the solvent in solutions of benzene, toluene, ethylbenzene, and p-xylene.     

Asymmetric Kumada-Corriu cross-coupling reaction with Pd2(dba)3 and an N-Ar axially chiral mimetic-type ligand catalyst

A catalyst comprised of Pd₂(dba)₃·CHCl₃ and an N-Ar axially chiral mimetic-type ligand, (S)-N-[2-(diphenylphosphanyl)naphthalene-1-yl]-2-(piperidinylmethyl)piperidine, provides good enantioselectivities for the asymmetric Kumada-Corriu cross-coupling reaction of 1-phenylethylmagnesium chloride and E-β-bromostyrene derivatives with which it is more difficult to achieve high enantioselectivity. Furthermore, in the case of styrene derivatives bearing both vinyl and aryl bromide groups, the chemoselective asymmetric cross-coupling reaction of the vinyl bromide group is observed. This N-Ar axially chiral mimetic-type ligand allows easy synthesis of a wide variety of analogues, and starting from the initial ligand, the enantioselectivity of coupling products is improved by modifying the structure in the ligand.     

Mechanism for the direct synthesis of tryptophan from indole and serine: a useful NMR technique for the detection of a reactive intermediate in the reaction mixture

The reaction mechanism for the biomimetic synthesis of tryptophan from indole and serine in the presence of Ac₂O in AcOH was investigated. Although the time‐course ¹H‐NMR spectra of the reaction of 5‐methoxyindole with N‐acetylserine were measured in the presence of (CD₃CO)₂O in CD₃CO₂D, the reactive intermediate could not be detected. This reaction was conducted without 5‐methoxyindole in order to elucidate the reactive intermediate, but the intermediate could not be isolated from the reaction mixture. Since the intermediate would be expected to have a very short life time, and therefore be very difficult to detect by conventional analytical methods, the structure of the intermediate was elucidated using a 2D‐NMR technique, diffusion‐ordered spectroscopy (DOSY). Two intermediates were detected and confirmed to be 2‐methyl‐4‐methyleneoxazol‐5(4H)‐one and 2‐methyl‐4‐hydroxymethyloxazol‐5(4H)‐one. The present results demonstrated that DOSY is a powerful tool for the detection of unstable intermediates. Copyright © 2010 John Wiley & Sons, Ltd.     

Double even tempering of orbital exponents: Application to Roothaan-Hartree-Fock calculations for He through Xe in Slater-type basis sets

Summary Double even tempering (DET) of orbital exponents is proposed as a useful generalization of even tempering (ET). The DET scheme uses two sets of basis functions for each angular momentum. The two sets have different principal quantum numbers and their exponents are generated by two different geometric sequences. Roothaan-Hartree-Fock (RHF) calculations on the atoms from He through Xe using both ET and DET Slater-type basis sets of the same size are carried out to demonstrate the substantial improvement offered by the DET scheme. The DET scheme reduces the maximum deviation of the RHF energies relative to the Hartree-Fock limit from 1.4 to 0.3 millihartrees.     

Subshell-pair correlation coefficients of atoms in momentum space

Angular correlation coefficients τ ^{nl,n^′ l^′} [p] between linear momenta of an electron in a subshell nl and another electron in a subshell n′ l′ are studied for the 102 neutral atoms He through Lr in their ground states, where n and l are the principal and azimuthal quantum numbers, respectively. We theoretically find that electron momenta are negatively correlated or uncorrelated; τ ^{nl,n^′ l^′} [p] < 0 when |l − l′|=1, while τ ^{nl,n^′ l^′} [p]=0 when |l − l′| ≠ 1. Numerical examinations of the atoms show that except for the He–B atoms, negative correlations are largest between 1s and 2p subshells, which have the most diffuse electron distributions in momentum space.     

Regioselective reactions of 1-alkylidene-2-oxyallyl cations with furan: control of [4 + 3] cycloaddition, [3 + 2] cycloaddition, and electrophilic substitution

The ring opening of alkylidenecyclopropanone acetal under acidic conditions produces the 1-alkylidene-2-oxyallyl cation as an intermediate, which reacts with furan to give the [3 + 2] and [4 + 3] cycloadducts as well as an electrophilic substitution product. The product distribution is controlled by the oxy substituents of the cation and by the solvent employed.     

Average inner product sums of electron linear momenta for atoms and ions

From the second moments of the electron-pair densities in momentum space, accurate Hartree–Fock values of the average inner product sum 〈∑ _i<j p _i ·p _j 〉 of electron linear momenta are evaluated for the 102 neutral atoms from He to Lr, the 53 singly charged cations from Li⁺ to Cs⁺, and the 43 stable anions from H⁻ to I⁻ in their experimental ground states. The present results are new for 38 species and improve the literature values for 68 species. Received: 18 July 2002 / Accepted: 4 September 2002 / Published online: 8 November 2002 Acknowledgement. This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education of Japan. Correspondence to: H. Matsuyama e-mail: hisashi@mmm.muroran-it.ac.jp