Phosphorus crystallographic data

The second problem concerns isomers of these various systems. As illustrated, 2d might be presumed to be planar. Unlike nitrogen, the inversion at phosphorus is very slow and there are, in fact, five possible isomers of it (three meso and two dl pairs). The interconversion of these isomers is reported in a subsequent paper by Davis, Hudson and Kyba along with x-ray crystallographic data on the structure of the so-called isomer B . 

Phosphorus. Early reports on the aromaticity of phospholes (Scheme 52) were controversial.152 X-ray crystallographic data show that 1,2,5-triphenylphos-phole has a nonplanar phosphole ring, while NMR, chemical, and thermodynamical data account for delocalization. Low inversion barriers of the phosphorus atom compared to the saturated congeners suggest nljz conjugation.153 154... 

In the absence of X-ray crystallographic data, 31P and 195Pt NMR spectroscopy is a useful method to investigate the nature of the products in the solution. In addition to earlier references to these topics, the Pople-Santry theory has been used to calculate the signs and relative magnitudes of the coupling constants for the type of phosphorus-bridged complexes covered in this section.1502... 

The theory proposed by Dewar et al. (154) is also based on a tr-bonded P—N skeleton of sp2-hybridized nitrogen and sp3-hybridized phosphorus but postulates a pair of linear combinations of phosphorus dxz and dy orbitals for overlap with an adjacent nitrogen p2 orbital. The result is a system of almost independent three-center 7t-bonds containing two phosphorus atoms and one nitrogen atom (Fig. 18). More detailed calculations appear to support this theoretical treatment (167,168,171, 172, 318) and indicate that conjugation beyond the three-center islands is of minor importance in cyclotriphosphazene derivatives (167). X-Ray crystallographic data for heterogeneously substituted cyclophosphazene derivatives (Section V,C) and evidence... 

The presence of a metal on a phosphoryl transferring-enzyme provides no assurance that the metal is directly involved in phosphoryl transfer. Thus with alkaline phosphatase, no direct interactions of Cl- with enzyme bound Zn2+ (69) or water with enzyme-bound Mn2+ (70) were detected by nuclear relaxation. Similarly no direct interaction of phosphate with enzyme bound Co2+ (71) or Mn2+ (71, 72) was detected by 31P nuclear relaxation. A Mn2+ to phosphate distance of 7.3 A was calculated from NMR data on the inactive Mn2+-enzyme (73) indicative of a second sphere complex. These results are in accord with crystallographic data on the enzyme which at 7.7 A resolution indicate that substrates cannot easily gain direct access to the metal site (74). More recent proton relaxation studies with the Cu2+ enzyme, which retains 5% of the activity, indicate the presence of a rapidly exchanging axial hydroxyl ligand on Cu2+ suggesting that the active metals may promote the nucleophilicity of the water molecule which is to attack the phosphorus (75). 

Hexagonal needles arranged in rosettes. Dec above lt00 . Practically insol in water, even when freshly prepd. Crystallographic data a0 9.425 C, 6.935 Ct/a, 0.736. use Prosthetic aid (artificial bone and teeth). theraP Cat Calcium and phosphorus supplement-... 

Although the PF and BF4 salts of the Te-dication (58) are stable solids, there is as yet no crystallographic data available. In addition to the NMR data given in Table 6 for the dication (58) and the precursor cyclic bis-telluride (59), a phosphorus absorption at S —143.0 (sept, Jpp = 712 Hz relative to H3PO4) is observed in the P NMR of the hexafluorophosphate salt of the dication (58). The drastic downfield shift observed in the Te NMR spectrum (8 1303.7) is consistent with the dication structure <91TL4537>. 

Summary Aryl ligands carrying oxygen, phosphorus or sulfur donor atoms in the side chain are introduced at silicon. Here we report on the synthesis of silyl chlorides and silyl triflates. The interaction between the silicon centre and the donor atom are discussed on the basis of NMR and X-ray crystallographic data. In the reaction of bis[2-(methoxymethyl)phenyl]methylsilyl triflate 8 with nucleophiles, reactivity of oxonium as well as of siliconium ions is observed. 

Contributions to the History of the Phosphorus Bases, Phil. Trans.y i860, cl, 408-533 crystallographic data by Quintino Sella of Turin, whose biography was written by Hofmann, (i), iii, 3-... 

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