Electron-accepting properties

Phosphoms pentafluoride behaves as a Lewis acid showing electron-accepting properties. It forms complexes, generally in a ratio of 1 1 with Lewis bases, with amines, ethers, nitriles, sulfoxides, and other bases. These complexes are frequently less stable than the similar BF complexes, probably owing to stearic factors. Because it is a strong acceptor, PF is an excellent catalyst especially in ionic polymeri2ations. Phosphoms pentafluoride is also used as a source of phosphoms for ion implantation (qv) in semiconductors (qv) (26). 

Wydeven [865] concludes that, in the presence of Co304 (6.8%), up to 60% of the reactant NaC103 decomposed in the solid state. During subsequent melting, there was an increase in reaction rate. The catalytic activity of the additive was ascribed to the electron accepting properties of the oxide (Co304 is a p-type semi-conductor). The apparent value of E increased from 120 to 200 kJ mole 1 between a = 0.05 and 0.5. 

If the cation moiety of the dissociative hydrocarbon has marked electron-accepting properties and the anion moiety is readily oxidized, a similar equilibrium is expected. An example has been found with hydrocarbon [28-2] (Komatsu et al., 1989 Okamoto et al., 1990). 

Carrier generation increases usually due to the electron accepting property of the sensitizer in its ground state or in its excited state. The detailed mechanism of the carrier generation is the subject to be reported in another symposium of the present meeting (lj. 

The electronic properties of n-conjugated polymers reflect well the basic electron-withdrawing or electron-donating properties of the components of the Ti-conjugated polymer [62]. In view of the electrochemical reduction potential, the thiophene unit and tetrathiafulvalene unit (Nos. 8 and 9 in Table 1) have a similar electronic effect in PAEs. It is reported that poly(arylenevinylene)s are also susceptible to electrochemical reduction [63, 64]. Due to the electron-accepting properties, PAEs are usually inert in electrochemical and chemical (e.g.,by I2 [54]) oxidation. 

Figure 14.7. Aromatic dianhydrides arranged in order of calculated electron affinity (EAjai) and C-NMR chemical shift of carbonyl carbon ( ( ). Larger EAd and smaller 6(. correspond to the strong electron-accepting property of a dianhydride.

E. Molecular Orbital Energies Electron-Donating and Electron-Accepting Properties. 250... 

Under appropriate conditions a proximate silicon atom may exhibit electron-donating or electron-accepting properties, stabilizing positive or negative charge. 

In addition to the stabilization of /1-carbocations, the /1-effect of silicon can also be observed in the ground states of neutral molecules. Lambert and Singer58 studied compounds of the type 42 where hyperconjugation should be enhanced by increasing the electron-accepting properties of the substituent X (MeO < Me < H < CN). o-tt overlap in this system gives the resonance structure 43 shown in equation 19. 

An interesting observation is that the differences between the nitro and sulfonyl electron accepting properties have less of an impact on the nonlinearity for the more highly conjugated stilbene compounds than they do in the case of the aniline systems. A similar effect also can also be seen in substituted polyenes. The calculated results for /3Z of A-(CH=CH2)n-NH2 (A = N02, S02CH3) are shown in Figure 2 as a... 

Increasing the electron-donor properties of the R, substituent in the case of dihydro derivatives of 1,2,4-triazolo[l, 5-a]pyrimidines [X, Z are N, Y is C(R)], tetrazolo[l, 5-a]pyrimidines (X, Y, Z are N), and pyrimidofl, 2-a]benzimidazoles (X, Y are o-C() I4, Z is N) tends to stabilize the B form. This can be explained by the conjugation of Rj with the electron-withdrawing azomethine group and the azole moiety. Reduction of the electron-accepting properties of the azole fragment (imidazopyrimidines and pyrazolopyrimidines) decreases the influence of the Ri substituent on tautomeric composition. 

This leads to a significant weakening of the electron donor properties of oxygen and to a significant weakening of the electron accepting properties of the silicon. This means that the heterolysis of a siloxane bond proceeds under much more severe conditions than their carbon analogues. 

The energies of these two essential orbitals give information, respectively, about the electron-donating properties or ionization potentials and the electron-accepting properties or electron affinities of the compounds. It can be seen that both methods predict that the four tautomers should have remarkably and somewhat surprisingly similar ionization potentials. As may be judged from the known ionization potential of the N(9)H tautomer, whose experimental value is 9.7 eV,98 the PPP-DBP method somewhat underestimates and... 

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