Calculations, bond dissociation energie

Fig. 32. Schematic potential energy diagram for the reaction of ground state Y(a2 D) with cis-2-butene. Energies of stationary points estimated from calculations on Y f C2H4.22 Energies of product asymptotes calculated from known thermodynamic values and calculated bond dissociation energies.22 31 34 156 157...

Summary Ab initio calculated bond dissociation energies of silicon compounds will be discussed by means of atomic ionization energies and atomic orbital overlap. Ring strain energies of C- as well as Si-rings are estimated by homodesmotic reactions. The hybridization concept is critically examined in the case of silicon compounds. From the most important results a set of basic rules will be presented. 

The calculated bond dissociation energy for 80 to form 81 and the azido radical is 55 kcal/mol. Since the bond dissociation energy for breaking the C—N bond in 80 is considerably lower than the energy of its triplet ketone ( 74 kcal/mol), it is feasible to break the C—N bond photochemically to form an azido radical and 82. The photorelease from 80 is an example of a photorelease from an excited state and thus it is fast enough to take place in crystals. 

In general, in ICP-MS, metal argide ions (MAr+) are observed at lower intensities compared to the dimeric metal oxide ions (MO+). Both ionic species correlate with the bond dissociation energies in the ICP or by the expansion of plasma in the vacuum. A correlation of measured oxide ion intensities (MO+) and experimentally determined or theoretically calculated bond dissociation energies of oxides has been found in laser mass spectra using a LAMMA 500 (laser microprobe mass analyzer, Leybold Hereaus AG, Cologne) by Michiels and Gijbels.52... 

Table 6.5. Calculated bond dissociation energies (BDE) of the various C-H bonds in the sugar moiety of dGuo. (Steenken et al. 2001) ...

The appearance potentials for molecular ions (ionization potentials) and for fragment ions formed in the mass spectra of metallocenes and related compounds are listed in Table XIII. These appearance potentials have been used to calculate bond dissociation energies and heats of formation of organometallic compounds, but the results obtained must be treated cautiously because the appearance potentials of fragment ions include excess energy due to excited species. The values obtained for the heats of formation are best considered as upper limits, rather than precise determinations. The extent to which energy due to excited states can contribute... 

Errede, L. A. Simple Equations for Calculating Bond Dissociation Energies, J. Phys. Chem., 64, 1031 (1960). 

Table 14 Calculated bond dissociation energies De (kcalmol" ) at B3LYP/6-311G(2d,p) of planar (D2h) and trans-bent (C2h) molecules E2X4 —2EX2 (E = C-Pb, X = H, F-I). The planar forms of the heavier compounds with E = Si-Pb, there are no minima on the potential energy surface...

Table 17 Calculated bond dissociation energies De of linear HE=EH —2 EH and excitation energies AEexc...

The indirect method was put forward by Stevenson in it the appearance potentials of the same ion produced from two different but related molecules are measured, and their difference is combined with thermochemical data to give the required dissociation energ) It is thus possible to calculate bond dissociation energies from appearance potentials and thermochemical data without a knowledge of ionization potentials. The essence of the method is to produce as the non-ionized partner in a dissociative ionization process of the type... 

Figure 20. ZnS-photocatalyzed dehydrodinierization of 2,5-DHF dependence of apparent product quantum yield on the calculated bond dissociation energy of the allylic C H bond.

The heats of formation for the radicals and for the trimer were estimated using a molecular orbital program MOPAC 7 with AM1 parameterization Hamiltonian for two different temperatures [22], The calculated bond dissociation energies are given in Table 2.2.6. 

For neutral molecules acting as bases, the effect of solvents would be similar to that of ions, but smaller in magnitude. That is, a hard acid solvent like water would deactivate other hard molecules more than related soft molecules. Table 1.7 lists the calculated bond dissociation energies for a number of complexes in the gas phase... 

The calculated bond dissociation energies are in good agreement with experiment except for difluorine. The theoretical result Dq = 46.0 kcaPmol is higher than the experimental value of Do = 36.9 kcaPmol. The trend however, that the BDE of F2 is smaller than the bond dissociation energies of CI2 and Br2 is preserved. Table 13.3 shows that the values of both and increase steadily from I2 to F2. We want to point out that... 

Table 1-1 Calculated bond dissociation energies for acetylene (I>o> kcal/mol) ...

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