Structures of tetrasilylmethane derivatives C(SiXMe2)4 (X = H, F, Cl, Br) in the gas phase and their dynamic structures in solution.

The structures of the molecules C(SiXMe2)4 (X = H, F, Cl, Br) have been determined by gas electron diffraction (GED). Ab initio calculations revealed nine potential minima for each species, with significant ranges of energies. For the H, F, Cl, and Br derivatives nine, seven, two, and two conformers were modelled, respectively, as they were quantum-chemically predicted to be present in measurable quantities. Variable-temperature 1H and 29Si solution-phase NMR studies and, where applicable, 13C NMR, 1H/29Si NMR shift-correlation, and 1H NMR saturation-transfer experiments are reported for C(SiXMe2)4 (X = H, Cl, Br, and also I). At low temperature in solution two conformers (one C1-symmetric and one C2-symmetric) are observed for each of C(SiXMe2)4 (X = Cl, Br, I), in agreement with the isolated molecule ab initiocalculations carried out as part of this work for X = Cl, Br. C(SiHMe2)4 is present as a single C1-symmetric conformer in solution at the temperatures at which the NMR experiments were performed

A Uniform Algorithm for All-Speed Shock-Capturing Schemes

There are many ideas for developing shock-capturing schemes and their extension for all-speed flow. The representatives of them are Roe, HLL and AUSM families. In this paper, a uniform algorithm is proposed, which expresses three families in the same framework. The algorithm has explicit physical meaning, provides a new angel of understanding and comparing the mechanism of schemes, and may play a great role in the further research. As an example of applying the uniform algorithm, the low-Mach number behaviour of the schemes is analyzed. Then, a very clear and simple explanation is given based on the wall boundary, and a concise rule is proposed to judge whether a scheme has satisfied low-Mach number behaviour

Structures of tetrasilylmethane derivatives (XMe2Si)2C(SiMe3)2 (X = H, Cl, Br) in the gas phase, and their dynamic structures in solution

The structures of the molecules (XMe2Si)2C(SiMe3)2, where X = H, Cl, Br, have been determined by gas electron diffraction (GED) using the SARACEN method of restraints, with all analogues existing in the gas phase as mixtures of C1- and C2-symmetric conformers. Variable temperature 1H and 29Si solution-phase NMR studies, as well as 13C NMR and 1H/29Si NMR shift correlation and 1H NMR saturation transfer experiments for the chlorine and bromine analogues, are reported. At low temperatures in solution there appear to be two C1 conformers and two C2 conformers, agreeing with the isolated-molecule calculations used to guide the electron diffraction refinements. For (HMe2Si)2C(SiMe3)2 the calculations indicated six conformers close in energy, and these were modeled in the GED refinement

A Photochemical Approach to the Gelsemine Skeleton

A silicon-tethered intramolecular meta photocycloaddition reaction was utilized to prepare a photoadduct, which was subsequently fragmented using m-CPBA to give a model for the skeleton of the alkaloid gelsemine

Isolation and characterisation ofCs-symmetryC60Me5O2OH, the first methylatedfullerenol; a bis-epoxide with two oxygens in a pentagonal ring

From the reaction between [60]fullerene and MeLi, we have isolated C60Me5O2OH, which has been characterised by both 1H and 13C NMR spectroscopy and by single-crystal X-ray analysis; uniquely, both epoxide groups bridge 5 : 6-bonds in the same pentagon

Electrophilic substitution of C60F18 into phenols: HF elimination between OH and a 1,3-shifted fluorine giving benzofurano[2',3':10,26]hexadecafluro[60]fullerene and derivatives

The reaction of C60F18 with phenol, 2-naphthol and quinol in the presence of ferric chloride leads to initial electrophilic substitution (aryldefluorination). This occurs at both ortho and para positions for phenol, at the ortho position for quinol, and at the relatively hindered but most reactive 1-position for 2-naphthol. It is followed, where sterically favourable, by HF loss either between the OH group and F (rendered adjacent as a result of a 1,3-shift) or to attack of the OH group at an adjacent double bond with loss of a beta-fluorine, giving benzofurano[2',3':10,26]hexadecafluoro[60]fullerene derivatives. The reaction is accompanied by some complete defluorination leading, in reaction with phenol and with 2-naphthol, to the formation of benzofurano[2',3':1,2][60]fullerene and naphtho[2,1:b]furano[d:1,2][60]-fullerene, respectively. The mechanism of base-catalysed reaction of phenols with C60Cl6 is re-evaluated

Self-organisation in P-substituted guanidines leading to solution-state isomerisation

Different isomeric forms of the amidine unit have been identified in Ph2P(E)C{NR'}{NHR'} (E=S, Se; R'=Pr-i, Cy), using both solid- and solution-state techniques

A Photochemical Approach to the Gelsemine Skeleton

A silicon-tethered intramolecular meta photocycloaddition reaction was utilized to prepare a photoadduct, which was subsequently fragmented using m-CPBA to give a model for the skeleton of the alkaloid gelsemine

[60]- and [70]Fullerenes are trifluoromethylated across 5 : 6-bonds

Trifluoromethylation of[60]- and [70]fullerenes occurs across both 6:6- and 5: 6- bonds giving unsymmetrical tetramethyl adducts having four contiguous CF3 groups; both fullerenes give bis adducts which do not involve 6: 6-addition, and unsymmetrical hexa-adducts (with contiguous CF3 groups) are also obtained from [60] fullerene

Coordination Chemistry of Isomeric Mixtures of Linked Di(phosphaguanidine) Compounds; a Spectroscopic and Crystallographic Study

Multinuclear NMR spectroscopy and X-ray diffraction techniques have been used to identify diastereomeric mixtures of rac- and meso-di(phosphaguanidine) compounds. A brief survey of their coordination chemistry has demonstrated the formation of N,N'-bound bimetallic aluminum species and monometallic platinum complexes in which the ligand chelates to the metal through the two phosphorus donor atoms