ESR. Spectra of the Radical Anion of Dimethyl-phenyl-phosphine

ESR. spectra of the radical anion (I^?) produced from dimethyl-phenyl-phosphine (I) both by electrolysis and reaction with alkali metals have been studied upon variation of temperature. The coupling constant assigned to the ³¹P nucleus depends strongly on temperature, whereas the coupling constants attributed to protons do not exhibit such a dependence. The π-spin populations at the benzene ring of I^? give evidence - in accordance with other experimental data [1] [2] – that the dimethylphosphino substituent is electron-attracting. This effect is thought to be due mainly to P ← C_π delocalization, which is analogous to the Si? C_π interaction in trimethylsilyl-substituted π-systems [3]. The ESR. spectrum previously [4] ascribed to I^? is shown to arise from a secondary radical. The formation and structure of this radical are briefly discussed.     

Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry detection: analysis of amino acid and organic acid trimethylsilyl derivatives, with application to the analysis of metabolites in rye grass samples

First, standard mixtures of trimethylsilyl (TMS) derivatives of amino acid and organic acid are analyzed by comprehensive two-dimensional (2D) gas chromatography (GC) coupled to time-of-flight mass spectrometry (GC × GC/TOFMS) in order to illustrate important issues regarding application of the technique. Specifically of interest is the extent to which the peak capacity of the 2D separation space has been utilized and the procedure by which the derivative standards are identified in the 2D separations using the mass spectral information. The resulting 2D separation is found to make extensive use of the GC × GC separation space provided by the complementary stationary phases employed.Second, in order to demonstrate GC × GC/TOFMS on two real sample types, trimethylsilyl metabolite derivatives were analyzed from extracts of common lawn grass samples (i.e., perennial rye grass), as a means to provide insight into both the pre and post harvest physiology. Various chemical components in the two rye grass extract samples were found to either emerge or disappear in relation to the trauma response. For example, a significant difference in the peak for the TMS derivative of malic acid was found. The successful analysis of various components was readily facilitated by the 2D separation, while a 1D separation would have produced too much peak overlap, thus impeding the analysis. The importance of using a GC × GC separation approach for the analysis of complex samples, such as metabolite extracts, is therefore demonstrated. The real-time analysis capability of GC × GC/TOFMS for multidimensional metabolite analysis makes this technique well suited to the high-throughput analysis of metabolomic samples, especially compared to slower, stopped-flow type separation approaches.     

Separation, recovery and recycling of a fluorous-tagged nickel catalyst using fluorous solid-phase extraction

Highly efficient separation, recovery and recycling of the fluorous-tagged catalyst, [Ni[F13C6C(O)CHC(O)C6F13]2], can be achieved with fluorous solid-phase extraction, after the Lewis acid catalysed synthesis of enaminodiones in conventional organic solvents.     

The radical anion of 1,2:9,10-dibenzo[2.2]paracyclophane.. An ESR,ENDOR, and TRIPLE resonance study

The radical anion of 1,2:9,10-dibenzo[2.2]paracyclophane ( 3 ) has been studied by ESR, ENDOR, and TRIPLE resonance spectroscopy under a variety of experimental conditions. The coupling constants of the eight protons in the deck-benzene rings, and of the four inner and four outer protons in the side-benzene rings are 0.234, 0.123, and 0.036 mT, respectively (solvent: 1,2-dimethoxyethane; counterion: K⁺). All three values have the same sign which is predicted to be negative. Comparison of the largest coupling constant (0.234 mT) with the corresponding value (0.297 mT) for the radical anion of the parent [2.2]paracyclophane ( 1 ) points to similar nodal properties of the singly occupied orbitals in and . Notwithstanding this similarity, seems to associate less readily than with alkali metal counterions, since tight ion pairs of with K⁺ are formed only in solvents of low solvating power. Effects of conformational changes on the ESR spectra, such as those previously observed for the radical anion of [2.2]paracyclophane-1,9-diene ( 2 ), are not apparent for in the temperature range of investigation. Hyperfine data are also reported for the radical anion of a derivative 4 which has a CH₃ substituent in one of the side-benzene rings of 3 .     

π-Spin distribution in the radical anion of benzo[2.2]paracyclophane and its relation to those in the radical anions of [2.2](1,4)naphthalenophanes

Radical anions of benzo[2.2]paracyclophane (V) and its 1,2,12,12,14,15,17,18-octadeuterio derivative (V-d₈) in three ethereal solvents (DME, THF and MTHF) and in the temperature range of ?90 to ?50° have been studied by ESR. and ENDOR. spectroscopy. The resulting hyperfine data provide a detailed picture of the π-spin distribution in V · ? which is in full accord with expectation. In particular, it is noteworthy that the naphthalene moiety accommodates almost the entire π-spin population, as may be anticipated by the higher electron affinity of this π-system relative to benzene. The proton coupling constants for V · ? have been compared with those values for the radical anions of anti- and syn-[2.2](1,4)-naphthalenophanes (II and III, respectively) which were obtained under conditions of low frequency electron transfer between the two equivalent naphthalene moieties. Such a comparison corroborates the interpretation of the results reported previously for II · ? and III · ?.     

Reactions of transition-metal carbonyls with anhydrous HF

The reactions of a wide range of transition-metal carbonyls with anhydrous HF are described. In particular, Ru₃(CO)₁₂, Os₃(CO)₁₂ and Ir₄(CO)₁₂ give the solution stable [Ru₃(CO)₁₂H]⁺, [Ru(CO)₅H]⁺, [Os₃(CO)₁₂H]⁺, [Os(CO)₅H]⁺ and [Ir₄(CO)₁₂H₂]²⁺ respectively, which have been characterised by a combination of ¹H and ¹³C NMR spectroscopy.     

Generating controllable atom-light entanglement with a Raman atom laser system

We introduce a scheme for creating continuous variable entanglement between an atomic beam and an optical field, by using squeezed light to outcouple atoms from a Bose-Einstein condensate via a Raman transition. We model the full multimode dynamics of the atom laser beam and the squeezed optical field and show that, with appropriate two-photon detuning and two-photon Rabi frequency, the transmitted light is entangled in amplitude and phase with the outcoupled atom laser beam. The degree of entanglement is controllable via changes in the two-photon Rabi frequency of the outcoupling process.     

Quantum chemical modelling case studies relevant to metal oxide dissolution and catalysis

Over the past 20 years quantum-chemical methods have been developed sufficiently so that they can now be applied to the elucidation of the complex mechanistic processes that occur during metal oxide dissolution and catalysis reactions. Many of the reactions occurring during these processes are not directly accessible to experimental techniques and therefore quantum-chemical modelling can be applied to probe the individual reaction steps involved in the overall mechanism. Quantum chemistry provides the means of calculating the electronic properties of solids (e.g. band structures) structural properties of solids and surfaces (for instance surface relaxation and rumpling) heats of formation and reaction, activation energies, spectroscopic excitation energies and vibrational frequencies. Three case studies are described, which have been chosen to cover a range of quantum chemical applications and methodologies. These case studies are a) the dissolution mechanism of MgO, b) the parameterisation of titanium dioxide for the determination of electronic properties and c) the mechanism and energetics of adsorption of Pd onto rutile. These case studies utilise Hartree-Fock semiempirical andab initio quantum-chemical methods as well as density functional methodologies. A range of model types are used, namely cluster models embedded in pseudo-atoms, 3-dimensional periodic models and 2-dimensional periodic surface models.