Gas-phase stability of cluster ions SF m + (SF6) n with m = 0–5 and n = 1–3

The gas-phase stabilities of cluster ions SF⁺_m (SF₆)_n with m = 0−5 were determined by using a high pressure mass spectrometer. The bond energies of SF⁺_m (SF₆)₁ were found to be less than 10 kcal/mol and to decrease with m = 0 → 5. There appear to be rather large gaps in the bond energies between n = 1 and 2 for the clusters SF⁺_m (SF₆)_n with m = 0−4. The structures of SF⁺₅, SF⁺ (SF₆)₁, SF⁺₃ (SF₆)₁, and SF⁺₅ (SF₆)₁ were investigated by ab initio molecular orbital calculations. For SF⁺₅, the D_3h geometry is found to be most stable andC_4v is a transition state of the Berry pseudorotation. For the ion-molecule complexes, the “on-top hat” models were found to be the most stable structures.     

Comparative study of the gas-phase bond strengths of CO2 and N2O with the halide ions

Thermodynamic data, ΔH _{n-1, n} ^o and ΔS _{n-1, n} ^o, for clustering reactions of halide ions X^?(X = F, Cl, Br, and I) with N₂Owere measured with a pulsed electron beam high-pressure mass spectrometer. In contrast to the fact that CO₂ forms a covalent bond with the fluoride ion to yield the fluoroformate ion, FCO₂ ^?, the interaction between F^? and N₂O is mainly electrostatic. It was found that the cluster ions F^? (N₂O)_n complete the first shell at n = 6, thus forming an octahedral structure. The difference between F—CO₂ ^? and F^? ... N₂O is discussed in terms of Coulombic, exchange, and charge-transfer interactions. The X^? (N₂O)₂ clusters (X = Cl, Br and I) are found to be of C_2h symmetry, while F^? (N₂O)₂ is of a twisted form and is slightly asymmetric due to a slight participation of covalency (charge transfer) in the core ion F^? ... N₂O.     

Repeat space theory applied to carbon nanotubes and related molecular networks. III

The present article is part III of a series devoted to extending the Repeat Space Theory (RST) to apply to carbon nanotubes and related molecular networks. In this part III, four problems concerning the above-mentioned extension of the RST have been formulated. Affirmative solutions of these problems imply (i) asymptotic analysis of carbon nanotubes (CNTs) via the new techniques of normed repeat space, Banach algebra, and C*-algebra becomes possible; (ii) a new linkage is formed between the investigations of CNTs and those of ‘spectral symmetry’. In the present paper, we give affirmative solutions to all of the four problems, together with (a) estimates of the norms of matrix sequences representing CNTs, (b) Challenging Problem A^#, which complements Problems A, (c) several pictures of ‘CNT Matrix Art’ which has heuristic power to lead one to get the affirmative answers to the problems formulated in an abstract algebraic manner.     

A significant role of alkaline cations on the Reimer-Tiemann reaction

The Reimer-Tiemann (R-T) reaction was investigated by DFT calculations. A model composed of CHCl(3), PhO(-)(Na(+))H(2)O and [NaOH(H(2)O)(2)](2) was employed for geometry optimizations. A K(+)-containing model was also investigated. The dichlorocarbene reagent, which has been thought of for a long time, was found to intervene only transiently in the carbenoid form. In this form, the Na(+) (or K(+)) coordination to CCl(2) enhances its electrophilicity toward C(6)H(5)O(-). The counter ion also works to stabilize the precursor phenoxide ion and intermediates of the substituted phenoxides in the hexagonal pyramidal coordination. The Na(+)-containing reaction consists of seven elementary processes, (K(+), six ones) with extremely high exothermicity and spontaneity.     

Role of hydrogen bonds in acid-catalyzed hydrolyses of esters

Acid-catalyzed ester hydrolyses were studied by means of DFT calculations. A model composed of ester and H₃O⁺(H₂O)₁₅ was adopted, and substrates esters are ethyl acetate, ethyl para-X-substituted benzoates (X?=?O₂N, Cl, H, iso-Bu, MeO, and Me₂N), and isobutyl benzoate. For the ethyl acetate, a stepwise path, precursor????TS1????Int1????Int2????TS2????product, was obtained. Here, TS is the transition state, and Int is the tetrahedral intermediate. The path is somewhat different from the established A_AC2 mechanism; the carbocation intermediate was calculated to be absent in the present model. The absence holds even for benzoates that may stabilize the cation except the X?=?Me₂N substituted one. At each local energy minimum, the cation character is retained in H₃O⁺. Proton relays along hydrogen bonds were found to prompt interchanges of covalent bonds. The rate-determining step is either TS1 for the electron-withdrawing X or TS2 for the electron-donating one.     

Development of New Strain Gage for High-Pressure Hydrogen Gas Use

The output changes of two conventional strain gages (Cu–Ni and Ni–Cr) and a newly-selected strain gage for high-pressure hydrogen gas use (Fe–Cr–Al) in 90 MPa hydrogen and nitrogen gases were measured under unloading conditions to find a high-performance strain gage for high-pressure hydrogen gas use. The changes in the outputs of the Cu–Ni and Ni–Cr gages in hydrogen gas were much larger than those in nitrogen gas, and the Fe–Cr–Al gage showed almost the same output changes in both gases. These results imply that the Fe–Cr–Al gage is superior to the others as a strain gage for high-pressure hydrogen gas use. A large amount of hydrogen entered the Cu–Ni and Ni–Cr foils, and the electrical resistances of these foils were significantly changed by hydrogen exposure, whereas almost no hydrogen entered the Fe–Cr–Al foil, and its electrical resistance was not changed. These resistance changes of the foils as a result of hydrogen entry were consistent with the gage output changes in hydrogen gas.     

Dynamic stability of silacarbonyl ylide

The structure of silacarbonyl ylide in the singlet gound state is obtained by ab initio quantum chemical calculations. This proves the recent experimental observation of silacarbonyl ylide by the photolysis of oxasilitane [W. Ando, K. Hagiwara, and A. Sekiguchi, Organometallics 6, 2270 (1987)]. The dynamic stability of the silacarbonyl ylide is studied by the TCSCF /3-21G ^(*) method. The second-order Jahn-Teller effect is examined in connection with the active role of frontier orbitals. Configuration analysis is used to clarify characteristic electronic structure of the silylene-carbonyl interaction.     

Electron localization in a finite one-dimensional chain

The localization characteristics of the electronic wave functions in a finite one-dimensional chain with the diagonal or the off-diagonal disorder of the potentials have been studied. It has been shown that the eigenfuction at the frontier level is relatively “strong” against the temptation to localize caused by the existence of the random potentials. It has also been pointed out that the spatial behavior of the total density reflects that of the diagonal random potentials, but that under the off-diagonal random potentials the total density is spatially uniform (completely extended).     

A FMO-controlled reaction path in the benzil-benzilic acid rearrangement

Reaction paths for the title rearrangement along with its methyl analogue were investigated by density functional theory calculations. The reaction model is R-CO-CO-R + OH(-)(H2O)4 --> R2C(OH)-COO- + (H2O)4 (R = Me and Ph), where the water tetramer is employed both for solvation to OH- and for the proton relay along hydrogen bonds. The reaction is composed of OH- addition, C-C rotation, carbanion [1,2] migration, and proton relay toward the product anions. The rate-determining step was calculated to be the carbanion migration. Apparently, carbanion [1,2] migration is unlikely relative to the carbonium ion one. However, LUMOs of the 1,2-diketones have large and nodeless lobes at the reaction center, the C1-C2 bond. The specific LUMO character is reflected both in the [2+1]-like one-center nucleophilic addition and in the carbanion [1,2] shift. The proton relay involved in the isomerization from the oxo intermediate to the carboxylate was calculated to take place via the water tetramer.