Doubly-charged gas phase cations

Unique features of doubly-charged stable organic ions are examined and the results correlated with experimental observations. Self-consistent field molecular orbital methods are used to compute structures and stabilities of C_nH ₂ ²⁺ (n=2–9) ions which are prominent in electron impact ionization of hydrocarbon molecules. A simple curve crossing model is employed to rationalize charge transfer reactions of these ions.     

FT-Raman spectroscopic investigation of a pseudopolymorphic transition in caffeine hydrate

The FT-Raman spectra of caffeine hydrate and anhydrous β-caffeine have been recorded. The accelerated dehydration of the hydrate has been monitored at 30, 35 and 40°C using an environmental chamber. The spectra representing the individual pseudopolymorphic phases differed subtly throughout the entire spectral range. Gradual broadening of the =CH stretching vibration observed at 3121 cm⁻¹ and the progressive appearance of a C=O stretch at 1656 cm⁻¹ were ascribed to intermolecular bonding between CH and C=O in the anhydrous phase. Accompanying loss of resolution of CH deformations in the lower wavenumber region observed at 1475 and 1255 cm⁻¹ supports the suggestion of intermolecular association involving CH. Concurrent loss of resolution of the weak C=N stretch at 1454 cm⁻¹ and recession of the medium intensity H---C=N deformation at 1255 cm⁻¹ were also detected, acknowledging the loss of interaction between N9 of the imidazole ring and the water molecule. The concomitant disappearance of the weak H₂O libration at 890 cm⁻¹ is observed, which suggests the occurrence of molecular realignment associated with corresponding loss of water of crystallisation. On removal of the hydrate backbone of the caffeine hydrate crystal structure, the lattice collapses, resulting in reduction of the intermolecular distance between individual caffeine molecules. The subsequent formation of a less rigid structure is evident, whereby molecules are weakly associated by unconventional CH…O interactions.     

Modeling of magic water clusters (H2O)20 and (H2O)21H+ with the PM3 quantum-mechanical method

The PM3 quantum-mechanical method is able to model the magic water clusters (H₂O)₂₀ and (H₂O)₂₁H⁺. Results indicate that the H₃O⁺ ion is tightly bound within the (H₂O)₂₀ cluster by multiple hydrogen bonds, causing deformation to the symmetric (H₂O)₂₀ pentagonal dodecahedron structure. The structures, energetics, and hydrogen bond patterns of six local minima (H₂O)₂₁H⁺ clusters are presented. © John Wiley & Sons, Inc.     

Mild,Redox-Neutral Formylation of Aryl Chlorides through the Photocatalytic Generation of Chlorine Radicals

We report a redox-neutral formylation of aryl chlorides that proceeds through selective 2-functionalization of 1,3-dioxolane through nickel and photoredox catalysis. This scalable benchtop approach provides a distinct advantage over traditional reductive carbonylation in that no carbon monoxide, pressurized gas, or stoichiometric reductant is employed. The mild conditions give unprecedented scope from abundant and complex aryl chloride starting materials.     

Magneto-photoluminescence of AlGaN/GaN quantum wells

The magneto-luminescence of GaN/AlGaN quantum wells in fields up to 52 T shows a field dependence that is strongly dependent on the well width. Strong redshifts are seen for the narrowest wells that are attributed to a Zeeman splitting. This is unexpected, since in bulk GaN epilayers the electron and hole g-factors of the lowest valence band cancel each other almost exactly. Therefore, we attribute this splitting to a reordering of the valence band due to the different band offsets caused by the strain and the aluminium component in the AlGaN barriers. The field dependence also gives information on the size of the exciton that has been converted into values for the exciton binding energy, and these values agree reasonably well with a theory that includes the presence of the electric field.     

Stability of high-energy N14H4(2+) ion and the effects of carbon and halogen substitution

Previous studies of oxygen addition into an N12 cage framework revealed the possibility of stable high-energy density materials (HEDM) resulting from such additions. In the current study, nitrogen addition into N12 is studied as a means of generating stable HEDM. Nitrogen addition into N12 is shown to yield an N14H4(2+) ion, which is examined by theoretical calculations to determine its stability with respect to dissociation. Other variations on this ion are generated by substituting carbon for nitrogen and/or halogens for hydrogen. The cage structures will be compared with respect to stability, and factors that enhance stability will be discussed.