X Bond Energies

Metal-X Bond Energies. In aqueous solutions at pH 0 the silver electrode is oxidized reversibly  

The gas-phase ionization potential for a silver atom is 7.6 eV. In contrast, water is oxidized (gives up an electron) at much lower potentials  

At a silver electrode the latter process is facilitated via formation of a Ag1— OH bond the shift in oxidation potential from +2.42 to +0.80 V is a measure of the bond-formation energy (—AGBF)  

the differential bond-formation energy [A(—AGBF)] (Ag—Cl bond energy, minus the energy required to break Ag—Ag bond at the Ag(s) surface) is given by the difference in oxidation potentials [Eqs. (10.7) and (10.8)]  

Because the escape energy for a Ag- atom from Ag(s) is 285 kJ mol-1, a reasonable approximation for the breakage of a single bond is 95 kJ mol-1 [(1/3)285 kJ].2 When combined with Eq. (10.9), this gives a reasonable value for — AGbf  

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The heat of formation of 804X4 was determined to be AH°f = +163 kcal mor. " Thus 804X4 is even more endothermic than S4X4 (AH°f = +110 kcal mok ). The mean E-X bond energies in E4X4 were estimated to be 59 kcal mol (E = Se) " and 72 kcal mol (E = S) from the enthalpies of formation. 

With regard to the stabilizing effect of the a-substituent at the silicon, the following gradation can be inferred from results of x-ray structures O > S > C > Cl. This sequence correlates with known Si-X bond energies. 

Fig. 11. The E—X bond energy should be enhanced in ligands which are delocalized...

What Pauling electronegativity is predicted for an element X if the ff-Xbond energy is 402 kj mol-1 The ff-ff bond energy is 432 kj mol-1 and the X-X bond energy is 335 kj mol-1. What would be the percent ionic character of the H-X bond If the molecular wave function is written as... 

Figure 8-5 Plot of C-X bond energies against H-X bond energies, using the data of Table 4-3...

The reactivity order also appears to correlate with the C-X bond energy, inasmuch as the tertiary alkyl halides both are more reactive and have weaker carbon-halogen bonds than either primary or secondary halides (see Table 4-6). In fact, elimination of HX from haloalkenes or haloarenes with relatively strong C-X bonds, such as chloroethene or chlorobenzene, is much less facile than for haloalkanes. Nonetheless, elimination does occur under the right conditions and constitutes one of the most useful general methods for the synthesis of alkynes. For example,... 

AH — X bond energies(reactants) - bond energies (pdts/TS)... 

It can be inferred from the data in table 9.10 that the decrease in reactivity can be explained in terms of decreasing Si-X bond length or increasing Si-X bond energy. 

The H-X bond energies calculated by the BOVB ab initio method. Calculated using Equation 6.20. 

Hydrogen replacement with benzene and the halobenzenes has been studied. The isomer distribution has been found to be very close to the statistical one and interpreted as the result of high-energy reactions. Halogen replacement yields increase in the series F-, C1-, Br- and iodobenzene showing dependence on the C—X bond energy both in liquid and in gas phase. 

FIGURE 5. Dependence of halogen (X) replacement by recoil211 At on the C—X bond energy in halobenzenes o—liquid, A—gas phase. Reproduced by permission of R. Oldenburg Verlag from Reference 27... 

Thermal 18F-for-X substitution yields have been measured in SF6-CH3X mixtures. Extrapolated to zero CH3X concentration, the absolute yields are found to increase with decreasing C—X bond energies (34) 0.11 0.2, 0.27 0.02, and 0.45 0.15% for X = Cl, Br, and I,... 

Consider the steps in the formulation above, and show that the trend in acid strengths is indeed set by the trend in H—X bond energies. 

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