Highlights

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MD calculations were performed for TATB crystal with high pressure.

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Cell parameters were consistent with the previous experiments and calculations.

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Intra- and inter hydrogen bonds were maintained with pressure.

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A unique structural change was observed in the range of 2.0 to 4.0 GPa.

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Difference TATB with DATB was discussed.

Highlights

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We observed two types of X-ray emission spectra in aqueous acetic acid.

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We reproduced the X-ray emission spectra via theoretical calculations.

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Theoretical data gave us electronic and molecular structure information.

Abstract

We calculated ionization potentials (IPs) to create single core–hole states and double ionization potentials (DIPs) to create double core–hole (DCH) states for a series of trihalosilyl–trimethylsilyl molecules bridged with hydrocarbons. From the calculated DIPs, IPs, and the hole–hole repulsion energies, we extracted the excess relaxation energies for the creation of DCHs at a single atomic site and interatomic relaxation energies for the creation of DCHs at two different sites. These excess and interatomic relaxation energies depend solely on the chemical environment around the atom(s) with core hole(s). We found that the interatomic relaxation is almost blocked by a dimethylene group (–CH₂CH₂–).

Abstract

We have investigated the K^–2, K^–1L^–1, and L^–2 double core hole (DCH) states of the SiX₄ (X = H, F, Cl, and CH₃) molecules using the CASSCF and DFT methods aiming at the DCH electron spectroscopy. The Si 1s IPs and DIPs of the present molecules and the generalized relaxation energies are compared and analyzed. The values extracted from the excess relaxation energy agree well with the generalized relaxation energy. The effect of the substituents (H, F, Cl, and CH₃) surrounding the central Si atom is examined. The present results illustrate that the DCH electron spectroscopy for K^–2, K^–1L^–1, and L^–2 DCH states is useful for the chemical analysis.

Ab initio molecular-orbital (MO) calculations were carried out, at the MP2/6-311++G(d,p)//MP2/6-31G(d) level, to investigate the conformational Gibbs energy of alkyl 1-cyclohexylethyl ketones, cyclo-C₆H₁₁CHCH₃COR (R=Me, Et, iPr, and tBu). In each case, one of the equatorial conformations was shown to be the most stable. Conformers with the axial CHCH₃COR group were also shown to be present in an appreciable concentration. Short CH⋅⋅⋅CO and CH⋅⋅⋅OC distances were found in each stable conformation. The result was interpreted on the grounds of CH⋅⋅⋅π(CO) and CH⋅⋅⋅O hydrogen bonds, which stabilize the geometry of the molecule. The ratio of the diastereomeric secondary alcohols produced in the nucleophilic addition to cyclo-C₆H₁₁CHCH₃COR was estimated on the basis of the conformer distribution. The calculated result was consistent with the experimental data previously reported: the gradual increase in the product ratio (major/minor) along the series was followed by a drop at R=tBu. The energy of the diastereomeric transition states in the addition of LiH to cyclo-C₆H₁₁CHCH₃COR was also calculated for R=Me and tBu. The product ratio did not differ significantly in going from R=Me to tBu in the case of the aliphatic ketones. This is compatible with the above result calculated on the basis of the conformer distribution. Thus, the mechanism of the π-facial selection can be explained in terms of the simple premise that the geometry of the transition state resembles the ground-state conformation of the substrates and that the nucleophilic reagent approaches from the less-hindered side of the carbonyl π face.

Ab initio MO calculations were carried out for the conformations of a series of alkyl-substituted benzyl alcohols C₆H₅CH₂CHOH−R (R = CH₃, C₂H₅, iPr, tBu) at the MP2/6-311G(d,p)//MP2/6-31G(d) level. It was found that the conformation where the OH group is gauche to the phenyl group is the most stable. The geometry where both the OH and R groups are close to phenyl is the second most stable. This finding has been interpreted on the grounds of the attractive OH/π and CH/π hydrogen bonds and a repulsive van der Waals interaction between vicinal CH groups. NMR nuclear Overhauser effects, spin-coupling data, and IR spectroscopic data are consistent with the conclusion given by the MO calculations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Ab initio MO calculations were carried out to examine the conformational energies of various benzylic compounds C₆H₅CH₂XR (X=O, CH₂, CO, S, SO, SO₂; R=CH₃, C₂H₅, iC₃H₇, tC₄H₉) at the MP2/6-311G(d,p)//MP2/6-31G(d) level. Rotamers with R/Ph in gauche relationship are generally more stable than the R/Ph anti rotamers. In these stable geometries, the interatomic distance in the interaction of α- or β-CH in the alkyl group and the ipso-carbon atom of the phenyl ring is short. The computational results are consistent with experimental data from supersonic molecular jet spectroscopy on 3-n-propyltoluene and NMR and crystallographic data on structurally related ketones, sulfoxides, and sulfones. In view of this, the alkyl/phenyl-congested conformation of these compounds has been suggested to be a general phenomenon, rather than an exception. The attractive CH/π interaction has been suggested to be a dominant factor in determining the conformation of simple aralkyl compounds.