Conformations of silicon-containing rings. 5. Conformational properties of 1-methyl-1-silacyclohexane: gas electron diffraction,low-temperature NMR,and quantum chemical calculations

The molecular structure of 1-methyl-1-silacyclohexane 3 has been determined by gas electron diffraction (GED). The conformational preference of the methyl group was studied experimentally in the gas phase (GED) and in solution (low-temperature (13)C NMR) and by quantum chemical calculations (HF, MP2, and B3LYP with 6-31G basis sets and mPW1PW91/6-311G(2df,p)). Both experimental methods result in a preference of the equatorial position of the methyl group, 68(7)% in the gas phase at 298 K and 74(1)% in solution at 110 K. The calculations predict 68-73% equatorial conformer at room temperature. From coalescence temperatures, Gibbs free energies of activation for ring inversion DeltaG++ (eq --> ax) = 5.81(18) and DeltaG++ (ax --> eq) = 5.56(18) kcal mol(-1) were derived. The calculated values for DeltaG++ (eq --> ax) are 5.92 (B3LYP) and 5.84 kcal mol(-1) (mPW1PW91).     

Hume’s Ontology

The paper claims that Hume??s philosophy contains an ontology, i.e. an abstract exhaustive classification of what there is. It is argued that Hume believes in the existence of a mind-independent world, and that he has a classification of mind-related entities that contains four top genera: perception, faculty, principle and relation. His ontology is meant to be in conformity with his philosophy of language and epistemology, and vice versa. Therefore, crucial to Hume??s ontology of mind-independent entities is his notion of ??supposing relative ideas??. Entities that are referred to by means of ordinary ideas can be truly classified, whereas entities that are referred to by means of relative ideas can only be hinted at. When Hume??s ontology is highlighted and systematised, his notion ??the faculty of imagination?? becomes highly problematic. However, the exposition also makes it clear that Hume deserves the honorary title: the first cognitive scientist.     

Functions and Shapes in the Light of the International System of Units

Famously, Galilei made the ontological claim that the book of nature is written in the language of mathematics. Probably, if only implicitly, most contemporary natural scientists share his view. This paper, in contradistinction, argues that nature is only partly written in the language of mathematics; partly, it is written in the language of functions and partly in a very simple purely qualitative language, too. During the argumentation, three more specific but in themselves interesting theses are put forward: first (in Section 3), there are more shapes than real numbers; second (in Section 4), the metrological notion ‘amount of substance’ can profitably be exchanged for ‘number of entities’; third (in Section 5), prototypical concepts will always be scientifically important.     

A polymer electrolyte containing ionic liquid for possible applications in photoelectrochemical solar cells

Various iodide ion conducting polymer electrolytes have been studied as candidate materials for fabricating photoelectrochemical (PEC) solar cells and energy storage devices. In this study, enhanced ionic conductivity values were obtained for the ionic liquid tetrahexylammonium iodide containing polyethylene oxide (PEO)-based plasticized electrolytes. The analysis of thermal properties revealed the existence of two phases in the electrolyte, and the conductivity measurements showed a marked conductivity enhancement during the melting of the plasticizer-rich phase of the electrolyte. Annealed electrolyte samples showed better conductivity than nonannealed samples, revealing the existence of hysteresis. The optimum conductivity was shown for the electrolytes with PEO:salt = 100:15 mass ratio, and this sample exhibited the minimum glass transition temperature of 72.2 °C. For this optimum PEO to salt ratio, the conductivity of nonannealed electrolyte was 4.4 × 10⁻⁴ S cm⁻¹ and that of the annealed sample was 4.6 × 10⁻⁴ S cm⁻¹ at 30 °C. An all solid PEC solar cell was fabricated using this annealed electrolyte. The short circuit current density (I _SC), the open circuit voltage (V _OC), and the power conversion efficiency of the cell are 0.63 mA cm⁻², 0.76 V, and 0.47% under the irradiation of 600 W m⁻² light.     

A phenomenological investigation of the shower particle pseudorapidity fluctuations in hadron-nucleus collisions

From the experimental matrix $\text{?(N}{}_{\mathrm{<mtext>g</mtext>}}\text{; n}{}_{\mathrm{<mtext>s</mtext>}}\text{, Δη}{}_{\mathrm{i}}\text{)}$ (the number of events with a given number N_g of particles with velocity 0.3c<v<0.7c, and n_s, the number of shower particles (v > 0.7c) in a pseudo-rapidity interval Δη_i) obtained from the Heidelberg-Igel hadron-nucleus experiment at CERN, we extract the shower particle multiplicity distributions as a function of ν, the number of nucleons that interacted with the projectile. We use a theoretically justified statistical correlation between ν and N_g (recoil protons) and the assumption that the correlation between n_s and N_g is given merely through ν. The data used are for incoming energies 50 and 150 GeV with a proton or pion as the projectile and Cu or Pb as the target. We find that the shower particle multiplicity distributions are of a Poissonian character in each η bin and for each value of ν. The average multiplicities $\text{〈n}{}_{\mathrm{<mtext>s</mtext>}}\text{〉(ν)}\text{Δη}{}_{\mathrm{i}}$ are approximately the same for the two targets and for the different projectile, possibly with a small excess for the pion projectile.The results are compared to a rather general theoretical model of the soft interaction type. The predictions from this model for the shower particle pseudorapidity distributions are very close to the derived values.     

Relative energy and structural differences of axial and equatorial 1-fluoro-1-silacyclohexane

The rotational spectra of the main isotopomer, of the (29)Si and of all (13)C isotopologues of axial and equatorial forms of 1-fluoro-silacyclohexane have been measured by conventional (only main species) and molecular beam Fourier transform microwave spectroscopy. r(0) and partial r(s) structures are given separately for the two forms. The main structural differences are discussed. From dipole moments and relative intensity measurements, a slight preference (E(Eq) - E(Ax) = 42 +/- 24 cm(-1)) for the axial conformer was found. The rotational spectra of some, the most intense, vibrational satellites have also been measured. They belong to the ring-puckering motions.     

13C NMR Investigation of Si-alkylsubstituted 1,3,5-Trisilacyclohexanes

¹³C NMR spectra of Si-alkylsubstituted derivatives of 1,3,5-trisilacyclohexanes have been recorded and analyzed. A systematic preparation of alkyl derivatives with mixed substituents made it possible to evaluate substituent-induced chemical shift (SCS) values for the ring carbon atoms in β and δ position. It is found that the β_e effect decreases in the order Me > Et > i-Pr > t-Bu. For the alkyl groups Me, Et, and i-Pr the β_a effect is smaller than the β_e effect. Axial SCS values for the t-Bu group are not accessible because chair conformations with an axial t-Bu group are unfavourable and tend to escape into a twisted boat form. The observed δ effects are small and do not show any obvious tendencies.