Pn Compounds

Formally unsaiuraicd PN compounds arc called phosphazenes and contain P in the... 

The corresponding chromium compounds [Cr(en)3]X3 evolve ethylenediamine [1131] and the values of E determined using non-isothermal measurements were 105 and 182 kJ mole 1 for X = Cl" and SCN", respectively. Hughes [1132] reported a value of E = 175 kJ mole"1 for X = Cl" and showed that the decomposition rate is sensitive to sample disposition. Amine evolution from both the (en) and propenediamine (pn) compounds was catalyzed by NH4C1 [1132,1133] or NH CN [1133,1285], addition of small amounts of these substances resulting in a substantial reduction of E. The influence of NH4C1 is ascribed [1132] to the dissociation products, since HC1 promoted the reaction but NH r and NH4I showed no such effect. 

The (en) compound developed nuclei which advanced rapidly across all surfaces of the reactant crystals and thereafter penetrated the bulk more slowly. Kinetic data fitted the contracting volume equation [eqn. (7), n = 3] and values of E (67—84 kJ mole"1) varied somewhat with the particle size of the reactant and the prevailing atmosphere. Nucleus formation in the (pn) compound was largely confined to the (100) surfaces of reactant crystallites and interface advance proceeded as a contracting area process [eqn. (7), n = 2], It was concluded that layers of packed propene groups within the structure were not penetrated by water molecules and the overall reaction rate was controlled by the diffusion of H20 to (100) surfaces. 

Dextrose used in PN compounding typically is provided as a 70% stock solution (70 g/100 mL), although some institutions use a 50% stock solution. The final dextrose concentration in the PN solution typically should not exceed 35%. Hydrous dextrose provides 3.4 kcal/g (14.2 kj/g). A dextrose infusion rate of 2 mg/kg per minute should be sufficient to suppress gluconeogenesis and prevent protein breakdown in adults.5 Continuous dextrose infusion rate in adult patients generally should not exceed 4 to 5 mg/kg per minute in most hospitalized patients.6,7... 

Oxygen-17 and Nitrogen-15. The pulsed Fourier-transform n.m.r. technique is providing a probe into the changes of environment of oxygen and nitrogen nuclei. For phosphoryl and PN compounds in particular, the data promise to provide information which will help clarify the information obtained from other nuclei. ... 

Restricted Rotation.—The PN compounds (65), in which the phosphorus atom bears electronegative substituents (X=hal or CF3) and the nitrogen atom bulky groups (Y=Bu or SiMes), exhibit rotational hindrance about the P—N bond at room temperature. " Four-co-ordinate compounds (66) and (67) exhibit lower barriers. -The possibility that n-a directional 7r-bonding also contributes to restricted rotation has been discussed. " Cyclophosphamide has been studied, " and evidence for... 

The related chromium compound [1140], trans-[Cr(pn)2Br2]Br H20, undergoes rapid dehydration at 395 419 K by a first-order process for which E = 96 kJ mole-1 and this is accompanied by some 10% isomerization to the cis compound. At higher temperatures, 433-473 K, the residual anhydrous trans compound isomerizes in the solid state this is also a first-order process and E = 180 kJ mole-1. 

In almost all compounds that have pn-dn bonds, the central atom is connected to four atoms or three atoms and an unshared pair and the bonding is approximately tetrahedral. The pn-dn bond, therefore, does not greatly change the geometry of the molecule in contrast to the normal tc bond, which changes an atom from tetrahedral to trigonal. Calculations show that nonstabilized phosphonium ylids have nonplanar ylidic carbon geometries, whereas stabilized ylids have planar ylidic carbons. ... 

It is clear that targeting only the combinations in this table, with no substitution of a trivalent lanthanide for the pnictide, Pn, there are 72 different reactions to monitor, for each sulfur or selenium and arsenic or antimony system, at varying temperatures (our compounds were prepared between 750 and 1200 °C). 

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