Gas-phase acidities of disubstituted methanes and of enols of carboxamides substituted by electron-withdrawing groups

The gas-phase acidities DeltaG degrees (acid) of some 20 amides/enols of amides RNHCOCHYY'/RNHC(OH)=CYY' [R = Ph, i-Pr; Y, Y' = CO(2)R', CO(2)R' ', or CN, CO(2)R', R', R' ' = Me, CH(2)CF(3), CH(CF(3))(2)], the N-Ph and N-Pr-i amides of Meldrum's acid, 1,3-cyclopentanedione, dimedone, and 1,3-indanedione, and some N-p-BrC(6)H(4) derivatives and of nine CH(2)YY' (Y, Y' = CN, CO(2)R', CO(2)R' '), including the cyclic carbon acids listed above, were determined by ICR. The acidities were calculated at the B3LYP/6-31+G//B3LYP/6-31+G level for both the enol and the amide species or for the carbon acid and the enol on the CO in the CH(2)YY' series. For 12 of the compounds, calculations were also conducted with the larger base sets 6-311+G and G-311+G. The DeltaG degrees (acid) values changed from 341.3 kcal/mol for CH(2)(CO(2)Me)(2) to 301.0 kcal/mol for PhNHC(OH)=C(CN)CH(CF(3))(2). The acidities increased for combinations of Y and Y' based on the order CO(2)Me < CO(2)CH(2)CF(3) < CN, CO(2)CH(CF(3))(2) for a single group and reflect the increased electron-withdrawal ability of Y,Y' coupled with the ability to achieve planarity of the crowded anion. The acidities of corresponding YY'-substituted systems follow the order N-Ph enols > N-Pr-i enols > CH(2)YY'. Better linear relationships between DeltaG degrees (acid) values calculated for the enols and the observed values than those for the values calculated for the amides suggest that the ionization site is the enolic O-H of most of the noncyclic trisubstituted methanes. The experimental DeltaG degrees (acid) value for Meldrum's acid matches the recently reported calculated value. The calculated structures and natural charges of all species are given, and the changes occurring in them on ionization are discussed. Correlations between the DeltaG degrees (acid) values and the pK(enol) values, which are linear for the trisubstituted methanes, excluding YY' = (CN)(2) and nonlinear for the CH(2)YY' systems, are discussed.     

Gravitational compression dynamics of charged colloidal crystals

We examine the compression of charged colloidal crystals under the influence of gravitational force by monitoring the spatiotemporal variations of Bragg diffraction from the crystal lattice. We use the dilute aqueous dispersions of colloidal silica particles (diameter=216 nm, charge number=733, a particle volume fraction φ=0.06) in the presence of 5-15 μM sodium chloride. The sedimentation profiles of the colloidal crystals along the crystal height are determined by in situ fiber optics reflection spectroscopy. The time evolutions of the sedimentation profiles are calculated by numerical simulations based on a phenomenological continuum model that explicitly incorporates the electrostatic interparticle interactions. The simulation results correctly describe the experiments at sufficiently high ionic strength.     

Novel Asymmetric and Stereospecific Aziridination of Alkenes with a Chiral Nitridomanganese Complex

The addition of pyridine N -oxide is necessary to obtain high enantioselectivities in the asymmetric aziridination of styrene derivatives through transfer of a nitrogen atom from chiral, toluenesulfonic anhydride activated nitridomanganese complex 1 [Eq. (a)]. Remarkably, high stereospecificity was observed in all the aziridinations of trans- and cis-1,2-disubstituted alkenes. R¹=H, Me, nPr, iPr; R²=H, Me; Ts=p-toluenesulfonyl.     

New Aspects of 1,3‐Diphosphacyclobutane‐2,4‐diyls

1,3‐Di(tert‐butyl)‐2,4‐bis[2,4,6‐tri(tert‐butyl)phenyl]‐1,3‐diphosphacyclobutane‐2,4‐diyl was formed from [2,4,6‐tri(tert‐butyl)phenyl]phosphaacetylene and t‐BuLi. In addition, the X‐ray diffraction analysis was carried out, together with theoretical calculations of the structure and NMR data.     

Ligand-ligand redox interaction through some metal-cluster units

The ligand-ligand redox interaction separated by di-, tri-, and hexanuclear cluster units is discussed in terms of the splitting of the redox waves (DeltaE(L)) and the comproportionation constants (Kcom(L)) of the ligand-based mixed valence state. Although two redox-active monodentate ligands in the mononuclear ruthenium(II) complexes (either cis or trans configurations) do not show appreciable splitting in their reduction waves, interestingly those separated by giant triruthenium and hexarhenium cluster units clearly show splitting. The molecular orbital considerations in the literature suggest that these units possess some pi-type molecular orbitals composed of metal dpi and possibly ligand ppi orbitals. Absence of the redox interactions in oxo-bridged diruthenium(II) and oxo-centered trirhodium(III) complexes where such pi molecular orbitals (including an antibonding one) are fully occupied, indicates the importance of empty pi* orbitals for the ligand redox communication.     

Effect of industrial water components on thermal stability of nitrocellulose

In order to prevent the spontaneous ignition of nitrocellulose (NC), NC is stabilized by washing with industrial water in its synthesis process. However, there is a possibility that the components in industrial water contribute to the thermal stability of NC. In this way, the purpose of this study is to clarify the effect of industrial water components on the thermal stability of NC. In experiments, a heat flux calorimeter was used to observe the thermal behavior of NC with the residue of vaporized industrial water. The induction period of heat release of NC with 2-mass% residues was approximately 2–5 h shorter than that of NC alone whose induction period was observed at 7 h. Those results indicate that the residue destabilized NC. On the other hand, when the additive amount of the residue was increased, the induction period gradually increased as well. Based upon these results, we assume that inorganic salts contributing to stabilization and destabilization competitively coexist in the industrial water components. The same thermal analysis was performed on NC with CaCO₃, CaSO₄, CaCl, ZnSO₄, NaCl, and CuCl. Those salts are predicted to exist in the industrial water. In the results, the induction period of NC with 2-mass% CaCO₃ was approximately 15-h longer than that of NC alone, while the induction period with the inorganic salts CaSO₄, CaCl, ZnSO₄, NaCl, and CuCl was 4–5-h shorter. Therefore, when the industrial water components accumulate in NC, the destabilization by inorganic salts such as CaSO₄, CaCl, ZnSO₄, NaCl, and CuCl and the stabilization by compounds such as CaCO₃ are thought to countervail against each other.     

Superionic Conduction in Co‐Vacant P2‐NaxCoO2 Created by Hydrogen Reductive Elimination

The layered P2‐Na_xMO₂ (M: transition metal) system has been widely recognized as electronic or mixed conductor. Here, we demonstrate that Co vacancies in P2‐Na_xCoO₂ created by hydrogen reductive elimination lead to an ionic conductivity of 0.045 S cm^?1 at 25 °C. Using in situ synchrotron X‐ray powder diffraction and Raman spectroscopy, the composition of the superionic conduction phase is evaluated to be Na_0.61(H₃O)_0.18Co_0.93O₂. Electromotive force measurements as well as molecular dynamics simulations indicate that the ion conducting species is proton rather than hydroxide ion. The fact that the Co‐stoichiometric compound Na_x(H₃O)_yCoO₂ does not exhibit any significant ionic conductivity proves that Co vacancies are essential for the occurrence of superionic conductivity.