With phosphorus-oxygen bonds

Problems still exist with AM 1, freatment of phosphorus-oxygen bonds is inaccurate, nitro compounds are still too positive in energy, and the peroxide bond, for example, is still too short. In many cases, l M3 is an improvement over AM 1,... 

Esters of penta- and trivalentphosphorus acids and their derivatives readily undergo cleavage of the phosphorus-oxygen bond under extremely mild conditions with formation of the phosphorus-fluorine bond Phosphates and phosphi-... 

Phosphorus can form five covalent bonds. The conventional representation of Pj (Pig. 10a), with three P—0 bonds and one P=0 bond, is not an accurate picture. In Pi four equivalent phosphorus-oxygen bonds share some double-bond character, and the anion has a tetrahedral structure (Fig. 10b). As oxygen is more electronegative than phosphorus, the sharing of electrons is unequal the central phosphorus bears a partial positive... 

This problem has been partially overcome by elimination of the phosphorus-oxygen bonds, as, for example, in the poly(phosphinoisocyanates), which have the structure shown in 6.47.42 It is also possible to form poly(metal phosphinates) with repeat unit -M(0PR20)2- by allowing a metal alkoxide to react with a phosphinic acid.43 Typical metal atoms are aluminum, cobalt, chromium, nickel, titanium, and zinc.43 Polymeric phosphine oxides can be prepared by the reactions... 

These reagents are usually prepared by treatment of a phosphine with an alkyl halide and successive addition of base, like BuLi or NaHMDS. Reaction with the ketone takes place by attack of the carbanionoid carbon of the ylide form on the electrophilic carbon of the carbonyl group via a four-membered heterocyclic transition state, the oxaphosphetane 35. The driving force for this transformation is provided by formation of the very strong phosphorus-oxygen bond. Subsequent collapse of the oxaphosphetane furnishes the desired exomethylene group under retention of geometry. 

The tribochemical film produces two major bands, one centered between 1130 cm"1 and 1185 cm"1 and one centered at 620 cm"1. Amorphous ortho- and pyrophosphate were prepared and their spectra seem to be consistent with the spectra of the tribochemical films. The films had two broad major bands consistent with the phosphorus-oxygen bonds. This indicates that the tribochemical film was not composed of phosphate glasses as expected, but rather predominantly amorphous orthophosphate or pyrophosphate formed by thermooxidative decomposition of zinc dialkyldithiophosphate. These groups may be connected by the metal cations. 

The unprotected 5-hydroxy group is then reacted with a 3-phosphoramidite derivative of the next nucleoside in the presence of tetrazole, which acts as a weak acid catalyst. (These phosphoramidite derivatives are now commercially available.) The diisopropylamino group is displaced by the 5-hydroxy group, and the phosphorus-oxygen bond is formed. 

White phosphorus reacts with oxygen to produce an oxide (P2O5). This oxide then reacts with any water that is around to form phosphoric acid. The phosphorus-phosphorus bonds of P4 are weak compared with the stronger phosphorus-oxygen bonds of P2O5 in other words, the oxide is thermodynamically much more stable than white phosphorus, and this drives the reaction to such an extent that white phosphorus spontaneously combusts in air. 

The analytical method used for parathion takes advantage of the ease with which the phosphorus-oxygen bond in that material is cleaved by hydroxide. The hydrolysis produces a mole of 4-nitrophenol for each mole of parathion originally present in solution. Because 4-nitrophenol has a well-defined absorption spectrum with a high molar absorptivity at the wavelength of maximum absorption (400 m/x) and because the reaction to form 4-nitrophenol from parathion is rapid and quantitative, the method provides a reliable and sensitive means for analyzing parathion. 

Although alkaline hydrolysis of monoalkyl or monoaryl phosphates is ordinarily very difficult, 2,4-dinitrophenyl phosphate, 2,4-(N02)2CaH30P03H2, does react with aqueous base, and with cleavage at the phosphorus-oxygen bond. Suggest an explanation for this. 

The P4O10 molecule has been studied in the vapour by e.d. with the results summarized in Table 19.5. The unshared (outer) 0 atoms are distinguished as O the (multiple) bond P-O is the shortest recorded phosphorus-oxygen bond. 

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