The Th fission valleys

One of the interesting problems in the nuclear fission studies is the nature of the asymmetry of the fission fragment mass distribution (FFMD). In connection with recent experiments, the valleys on the potential energy surface of ²²⁶Th have been considered. The pre-scission nuclear shape calculated as a result of the minimization in multi-dimensional space of the deformation parameters with two constrains is shown to be of the type considered by Brosa et al.     

硅p-n结太阳电池对DF激光的响应

 对硅p-n结太阳电池在DF激光辐照下的响应进行了理论和实验研究。推导了p-n结反向饱和电流随温度的近似变化关系。根据该近似关系，计算了太阳电池在DF激光辐照过程中输出电压的变化曲线。计算结果和实验结果之间取得了比较好的一致性。     

Halogens in γ-position enhance the acidity of alkyl aryl sulfones and alkane nitriles

On the basis of measuring the rates of base-catalyzed deuterium exchange the pK_a values of a series of 3-halopropyl aryl sulfones and 4-halobutyronitriles were estimated. It was shown that halogen substituents, although separated from the carbanionic site, exert a substantial carbanion stabilizing effect. These effects were rationalized by DFT calculations.     

An analysis of states in the phase space: the diatomic molecules

Summary The paper concerns a theoretical model to calculate the number of allowed states for the electrons in the diatomic molecules through the quantum-statistical analysis of the phase space. The approach is a straightforward extension of that already discussed in the case of many-electron atoms. Simple formulae are derived that enable to calculate the dissociation energy, bond length and vibrational frequency of diatomic molecules in a good agreement with the experimental data.     

Modeling NMR chemical shifts: a comparison of charge models for solid state effects on N chemical shift tensors

This paper presents results from applying different point charge models to take into account intermolecular interactions to model the solid state effects on the ¹⁵N NMR chemical shifts tensors. The DFT approach with the BLYP gradient corrected exchange correlation functional has been used because it can include electron correlation effects at a reasonable cost and is able to reproduce ¹⁵N NMR chemical shifts with reasonable accuracy. The results obtained with the point charge models are compared with the experimental data and with results obtained using the cluster model, which includes explicitly neighboring molecular fragments. The results show that the point charge models can take into account solid state effects at a cost much lower than the cluster methods.     

“Truncated” Pagodanes — Synthesis of Functionalized [1.1.1.1] and [1.1.1.0] Pagodanes

“Truncated” [1.1.1.1] pagodanes like the [1.1.0.0] and [0.0.0.0] homologues3 and 4 (E_Str = 146.1 – 171.5 kcal mol^?1, MM2) are potential precursors of unusual unsaturated homoconjugated radical cations and σ-bishomoaromatic dications. Attempts are presented toward the synthesis of 3 - starting out from [1.1.1.1] pagodane-4,9-dione 9 and diaza [2.2.1.1] pagodadiene 11 by cycloelimination (unsuccessful) and by Favorskii-type ring contraction methodologies. Control experiments with the model diketone 19 documented the limitations for α,α′-difunctionalization of 9 as the prerequisite for one-pot double Favorskii-type ring contraction. A de novo synthesis for such α,α′-disubstituted derivatives of 9(54) was not sufficiently expeditious to open a practical access to 3. Sequential double bridgehead hydroxylation of 9, successfully practized with model 19, similarly suffered from inherent cage effects and allowed only limited yields of [1.1.1.0] pagodanone 10, the intermediate on the way to 3.     

Kinetic isotope effects of nitrogen and hydrogen in reaction of N-tert-butyl-P-phenylphosphonamidothioic acid with alcohols

Nitrogen and hydrogen isotope effects for the reaction of N-tert-butyl-P-phenylphosphonamidothioic acid 1 with alcohols (methanol, butanol, iso-propanol, tert-butanol) were measured in dichloromethane at 30 °C. The observed nitrogen isotope effect k₁₄/k₁₅ is only slightly sensitive to a steric hindrance of the alcohol [1.0070 ± 0.0002 (MeOH), 1.0074 ± 0.0004 (BuOH), 1.0062 ± 0.0004 (PrⁱOH), 1.0087 ± 0.0007 (Bu^tOH)]. The pre-equilibrium step, with proton transfer from oxygen to nitrogen was proved by the inverse hydrogen effect k_ROH/k_ROD[0.778 ± 0.052 (MeOH), 0.863 ± 0.063 (BuOH), 0.883 ± 0.080 (PrⁱOH), 0.746 ± 0.084 (Bu^tOH)]. The experimental values are consistent with theoretical results of semiempirical calculations on PM3 level for an elimination-addition mechanism and metathiophosphonate PhPSO intermediacy. For the reaction with methanol the addition-elimination mechanism is also possible.     

Semiempirical quantum chemical calculations of molecular π- complexes

A method is suggested to calculate the geometrical and thermodynamical characteristics of organic π- complexes. The interaction energy is considered as a sum of two terms: the specific quantum chemical interaction of the π- electron systems depending essentially on the chemical nature of reactants, and the nonspecific atom-atom (van-der-Waals) interaction depending only on the kind of atoms belonging to the fragments of a complex. An attractive quantum chemical interaction is described in terms of the PPP-method; the van-der-Waals interaction is expressed in terms of the empirical exp-6-potential. The geometries of complexes are found by the complete energy minimization with respect to six parameters characterizing the mutual orientation of the complex fragments. Energies, entropies and equilibrium constants of several tetracyanoethylene π-complexes are calculated by this method. The results agree satisfactorily with experimental data.     

Consistent force field calculations on the geometry of triethylamine

Consistent force field calculations on the geometry of triethylamine are presented and compared with experimental results. Triethylamine seems to exist mainly in a conformation with all ethyl groupscis to the lone pair electrons at the nitrogen atom.

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Kraftfeldberechnungen der Geometrie von Triethylamin (Kurze Mitteilung)

Zusammenfassung Consistent Force Field Rechnungen der Geometrie von Triethylamin werden mit experimentellen Ergebnissen verglichen. Triethylamin existiert dann in der günstigsten Konformation, wenn alle Ethylgruppencis zum einsamen Elektronenpaar des Stickstoffs stehen.