Leading invariant

The ubiquity of compounds of the type P(X)(Y)(Z), together with the lone pair on the phosphoms leads invariably to a vast array of concomitant compounds of the type (A)P(X)(Y)(Z), wherein the phosphoms exhibits CN of 4. Thns the enormous range of phosphanes of the type PR3, coupled with their ability to coordinate with metal centers and the many catalytic properties of the resulting complexes, ensures that 4-coordinate phosphoms is of utmost chemical and industrial importance. Away from metal chemistry, POCI3 and P4S10 also exhibit 4-coordinate phosphoms atoms and, as we will see, they both have enormous technological relevance. The basic geometry for phosphoms of CN 4 will be tetrahedral. 

Although the precise mechanism of the coupling reaction is not thoroughly established, one can visualize the formation of (71) as arising from initial fragmentation of the C(16)—C(21) bond of (69), followed by condensation of vindoline with the more accessible a face of the iminium ion (73). The impact of the Polonovski approach in this area is emphasized by the fact that all other attempts to couple vindoline with 16,21-seco derivatives of catharanthine lead invariably to formation of the unnatural dimer. A Polonovski reaction was also a key step in the subsequent elaboration of anhydrovinblastine (71) to (68). ... 

To separate the product from unreacted HgO, the azide is dissolved by heating and then filtered. It recrystallizes as the above-mentioned, highly sensitive needles which have to be handled with extreme caution e.g., a large particle, slowly sinking in a water-filled beaker, exploded when touching the bottom [13]. Likewise, crystals adhering to the wall could not be removed without explosion. It is essential to move the liquid constantly with a stirrer made of a soft material [13], as slow cooling of an unstirred solution leads invariably to explosion [224],... 

To cope with finite boundaries, we next introduce the separation of variables method. This method is thus capable of attacking boundary value problems and leads invariably to sets of ODE (rather than a single one). Since only linear equations are amenable to this method, we can obviously invoke the principle of superposition. This means that solutions of sets of ODE can be summed to... 

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