Bond energies carbon-phosphorus

The comparison of the bond energies in boron, silicon, phosphorus and arsenic atoms with that of carbon atoms supports this idea (Table 2). 

The effect of temperature on the aryl interchange between TPP and TRI was studied between 100 and 140°C, to make sure that these equilibrium constants developed from probability analysis apply at all temperatures, and to estimate an activation energy for these reactions. The technique of using probability analysis to calculate chemical equilibrium constants, presumes that these "constants" are independent of temperature. That is, the various aryl interchange reactions are presumed to be thermally neutral, and the breaking of the various carbon-phosphorus bonds requires the same amount of energy. 

Catenation is defined as the self-linking of an element to form chains and rings. Carbon, then, given the above discussion, is the all-time champion catenator, much better than silicon (or sulfur, boron, phosphorus, germanium, and tin, the other elements that show this ability). Why should this be so A comparison of the relevant carbon and silicon bond energies as shown below is helpful ... 

Phosphorus—Carbon Bond. The P—C bond is 0.184—0.194-nm long and has an energy of ca 272 kj/mol (65 kcal/mol). It is one of the more stable bonds formed by phosphoms, resistant to both hydrolysis and oxidation (7,8). Unlike the phosphoms—halogen or phosphoms—oxygen bonds, the P—C linkage is inert to exchange. A phosphoms atom connected to carbon behaves similarly to another carbon atom in a hydrocarbon chain. 

The r-delocalisation in the parent phospholide anion I (Fig. 3, R =R =H) can be expressed in the valence bond picture by resonance between the canonical structures lA-IC (and their mirror images). Phosphonio-sub-stituents (R =R =PH3 ) increase the weight of the 1,2-dipolaric canonical structure IB and induce thus, in essence, a partial r-bond localisation and a shift of r-electron density from the phosphorus to the adjacent carbon atoms [16]. Consequences of this effect are the decrease in delocalisation energy for reaction (1) depicted in Fig. 4, and lower C2-C3/C4-C5 and higher C3-C4 bond orders which are reproduced in concomitant variations of computed bond distances [16]. 

In vinylphosphinidine, the open- and closed-shell singlets lie 17 and 23 kcal/mol above the ground triplet state. The energies of the two singlet states of vinylphosphinidine are comparable because electron-electron repulsion in the 3p orbitals is reduced and because the overlap of 2p and 3p orbitals of carbon and phosphorus is poor and the resulting carbon-phosphoms double bond is relatively weak. ... 

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