Yosuke Yoshimura

Chemical reaction in medium density fluid. Solvent density effects on the dimerization equilibrium of 2‐methyl‐2‐nitrosopropane in carbon dioxide

The dimerization equilibrium of 2‐methyl‐2‐nitrosopropane in carbon dioxide was studied in a wide range of solvent density from 200 to 1100 kg m−3 at 25.0 and 35.0 °C. We found an inversion of the density dependence of the equilibrium constant. The configurational volume change for the dimerization has a large positive value in the medium density region, although it is negative in the high density region as usually observed for the bond formation reactions in the liquid state. This anomaly is reproduced by the cavity distribution function calculated from the integral equation based on the HNC or PY approximation for the Lennard‐Jones fluid model. The large positive value in the medium density region is interpreted in terms of desolvation effect due to the dimerization. The long‐range correlation between molecules due to attractive forces is suggested to play an important role in determining the reaction volume in the medium density region.

Metathesis‐like Splitting Reactions of Metallated [36]Octaphyrins(1.1.1.1.1.1.1.1): Experimental and Computational Investigations

meso-Octakis(pentafluorophenyl)-substituted [36]octaphyrin(1.1.1.1.1.1.1.1) (1) is a figure-of-eight nonaromatic macrocycle that serves as a unique platform to induce a metathesis-like splitting reaction upon bis-Cu(II) metalation. To get a better understanding of this splitting reaction, we examined the metalation of 1 with several metal ions. In contrast with the smooth and quantitative splitting reaction of bis-Cu(II) complex 1-CuCu, free-base 1, mono-Cu(II) complex 1-Cu, and bis-Zn(II) complex 1-ZnZn do not undergo the splitting reaction. Mono-Co(II) complex 1-Co was selectively produced from metalation with the Co(II) ion, from which hybrid complex 1-CoCu was synthesized. The hybrid complex 1-CoCu undergoes the splitting reaction to give 2-Co and 2-Cu quantitatively. Activation parameters of the splitting reactions were determined: E(a)=104 kJ mol(-1), DeltaH(double dagger)=101 kJ mol(-1), DeltaS(double dagger)=-25.0 J mol(-1) K(-1), and DeltaV(double dagger)=18 cm(3) mol(-1) for 1-CuCu and E(a)=105 kJ mol(-1), DeltaH(double dagger)=102 kJ mol(-1), and DeltaS(double dagger)=-29.9 J mol(-1) K(-1) for 1-CoCu. A marked difference between the splitting reaction reactivity of 1-CuCu and 1-ZnZn has been examined by DFT calculations at the B3LYP/631SDD//B3LYP/LANL2DZ level, which revealed that the reaction proceeds through a stepwise route involving initial C1-C20 bond formation to give INT1 as the rate-determining step and subsequent C21-C40 bond formation to give a spirocyclobutane intermediate (INT2), followed by a radical reverse cycloaddition reaction to give two metalloporphyrins. Inherent instability of 1-CuCu, which may arise from its strongly distorted structure, was indicated to be a main factor in the smooth splitting reaction. Finally, a new bis-Pd(II) complex (5-PdPd) was isolated in the metalation of 1 with Pd(OAc)(2) in a 9:1 mixture of 2,2,2-trifluoroethanol and methanol as a manifestation of the transannular electronic interaction in metalated octaphyrin complexes. Collectively, these results underscore the importance of the transannular electronic interactions that are enhanced by metalation, depending upon the coordinated metal ions.

Solute-solute potential of mean force in simple fluids at infinite dilution

The effects of solvent density on the solute-solute potential of mean force in Lennard-Jones fluids are studied by means of the integral equation method. The solvent density plays an important role in solute-solute correlation in solution: the effect of the solute-solvent attractive interaction is quite different in the medium-density and high-density regions. In the latter the strong solute-solvent attractive interaction destabilizes the contact solute pair, and the strong solvent-solvent attractive interaction stabilizes the contact solute pair, which is expected from both ‘desolvation’ and the ‘solvophobic’ effect. In the medium-density region, however, curious phenomena are observed that cannot be interpreted by a simple picture: for example, the solute-solvent attractive interaction stabilizes both the solvent-separated pair and the contact pair of solute molecules under some conditions. The characteristics of the medium-density region are discussed in terms of the density fluctuation around the solu...

Chemical equilibrium in simple fluids: Solvent density dependence of the dimerization equilibrium of 2‐methyl‐2‐nitrosopropane in argon and xenon

We have studied the dimerization equilibrium of 2‐methyl‐2‐nitrosopropane (MNP) at 60 and 35 °C in argon and xenon up to densities about twice the critical density of the solvent. With an increase in the solvent density, the dimerization equilibrium constant at 60 °C decreases in the low‐density region, whereas it increases in the high‐density region. The inversion of the density dependence occurs around ρr≂0.8 in argon and ∼1.4 in xenon, where ρr means the density reduced by the critical density of the solvent fluid. The equilibrium constant in xenon at 35 °C increases with increasing solvent density in the low‐density region (ρr<∼0.5), while it decreases in the medium‐density region (0.5<ρr<1.5). The equilibrium constant in argon at 35 °C has a similar density dependence to that at 60 °C. The internal energy change for the dimerization shows a large density dependence in the low‐density region of xenon, while it changes little with density in argon. The theoretical calculation by the Percus–Yevick (PY) ...

Solvophobic interaction in a simple associated fluid : a study on the basis of Wertheim's theory on associated fluids

We apply Wertheims theory on the associated fluid (1984, J. stat. Phys., 35, 19) to the study of the solvophobic effect in the simplest associated fluid where the dimer and the monomer molecules are in equilibrium. We calculate numerically the radial distribution function between hard sphere solute molecules in a simple associated fluid by means of integral equations. The results show that the solvent association alone does not bring about a significant solvophobic interaction between solute molecules, if compared with the hard sphere solvent at the same density. The results are interpreted as the competition of two effects, the solvophobic effect and the packing effect.

Bond-number distribution of a solute molecule in the hard-sphere fluid

The validity of the bond-number (coordination-number) distribution of a molecule in a fluid is studied for a solute molecule interacting with solvent molecules through a square-well potential. The bond number is defined as the number of solvent molecules in the square well. The effect of the strength of the solute-solvent interaction on the chemical potential of a solute molecule is expressed rigorously by a moment generating function of the bond-number distribution of a reference system in which the solute molecule behaves as a hard sphere. A cumulant expansion of the generating function gives an expansion of the chemical potential of the solute molecule around a reference value. The characteristics of the bond-number distribution, and the validity of the statistical mechanical relations are demonstrated for a hard-sphere solvent over a wide density region by Monte Carlo calculations. The average bond number of the reference system increases almost linearly with increasing density, although the variance ...

Keto‐enol tautomeric equilibrium of acetylacetone in trifluoromethane near the critical temperature

The keto‐enol tautomeric equilibrium of acetylacetone in trifluoromethane were studied at 300±0.5 K (1 K above the critical temperature) from 130 kg m−3 to 800 kg m−3 by using FT–NMR. No anomalous behavior near the critical point has been found within the experimental error. The equilibrium constant decreases rapidly in the low density region (<200 kg m−3) and the decreasing rate reduces with increasing the density of solvent. The density dependence is interpreted by the hydrogen bonding between trifluoromethane and acetylacetone.

Optical and x-ray studies of thin mixed crystals of NaCl-typed RbI and CsCl-typed CsI

Thin Rb1−xCsxI mixed crystals have been grown from the melt in a very small gap formed in between a pair of quartz plates and reflection spectra were measured in the uv-light region at low temperature. Continuous spectral changes of the exciton bands with the composition x suggest strongly the formation of extended solid solution both in the RbI-rich (0.0⩽x⩽0.4) and CsI-rich (0.7⩽x⩽1.0) regions. The formation was confirmed by x-ray diffraction, and the compositional change of the lattice constant was determined. These results are in contrast to the eutectic type phase relation with only a limited solid solubility observed in the bulk state of the RbI–CsI binary system.

Mean Force Acting on a Thin Hard Needle in a Hard Disk Fluid

Non-linear behavior of the chemical potential of a two-dimensional infinitely-thin hard needle with respect to the needle length in a hard disk fluid is studied. The expansion of the chemical potential with respect to the needle length shows that the mean force acting on the needle along the needle axis, i.e. the needle length derivative of the chemical potential with the reverse sign, is dependent on the needle length. Damped oscillatory behavior of the mean force was found by a Monte Carlo calculation with the insertion-and-elongation procedure. The pair distribution function between the needle and the hard disk changed drastically with the needle length.

Hundreds of collisions between two hard needles

We found that two thin hard needles can collide hundreds of times without any additional forces. The number of collisions is sensitive to the initial conditions, especially the rotational phase of each needle. Long continuation of the chattering collision takes place at a limited region in the parameter space. The scattering angle was almost constant for the collision number in a frequent chattering collision, while the change in the collision number in a short chattering collision brings about a sizeable perturbation on the scattering process.