BDE bond dissociation enthalpy

The first of the more significant terms in (4) is the bond dissociation enthalpy (BDE) D(R - X), the variation of which for a number of methyl derivatives is shown in Figure 1 [19]. It can be seen that by changing X from fluoride to iodide with R = CH3, AH8e will become less positive by approx. 240 kj mol 1 for R = CH3CO the same change makes AHge less positive by approximately 290 kj mol"1. 

A variety of bond dissociation enthalpies at 298 K have been calculated at the G2MP2, CBS-Q and G2 levels of theory and a summary of typical 0-0 BDEs are presented in Table 1. It becomes immediately obvious that the estimate of the 0-0 BDE of a generic peroxide should be iucreased by 10 kcalmoD to ca 44 kcalmoE . 

Determination of the acidities of eight enols R1R2C=C(OH)R3 in DMSO and the oxidation potentials of then conjugate bases have permitted the estimation of the corresponding H—O bond dissociation enthalpies since BDEha = 1.37pXwA + 23.1 ox(A ) + 73.3 kcal mol-1.129 The results have been discussed in terms of steric and electronic effects. For MeS2C=C(OH)R, pAfrA increases, E0X(A ) becomes more negative, and BDE decreases with the bulk of R. 

It is our belief that the evidence is overwhelming that there is a conformational trigger responsible for Co—C bond homolysis. The central issue is the nature of the mechanism. Prior to assessing possible mechanisms in more detail, we first briefly review information on Co—C bond dissociation enthalpies (BDEs) for Bl2 derivatives and Bi2 models in solution and relate this information to other well-established properties of these organocobalt species. 

The prediction of the homolytic bond dissociation enthalpy (BDE) and adiabatic ionization potential (IP) of 4-hydroxy-2,2,3,5,6-pentamethylbenzoselenete and benzotelluretes has been calculated <20060BC846>. 

The bond-dissociation enthalpy (BDE, also called bond-dissociation energy) is... 

Peroxides are often added to free-radical reactions as initiators because the oxygen-oxygen bond cleaves homolytically rather easily. For example, the bond-dissociation enthalpy of the O —O bond in hydrogen peroxide (H —O —O —H) is only 213 kJ/mol (51 kcal/mol). Give a mechanism for the hydrogen peroxide-initiated reaction of cyclopentane with chlorine. The BDE for HO — Cl is 210 kJ/mol (50 kcal/mol). 

Bond dissociation enthalpies (BDEs see Box l.l) for transition metal o-organyls appear at present to fall within the quite wide range of 70-330 kJ mol-1, i.e. a range comparable to those of main group alkyls. It should be noted, however, that transition metals also have the possibility of including a 7t-component when the carbon is sp2 (alkylidenes, alkenyls, acyls) or sp hybridized (alkylidynes, vinylidenes, alkynyls), thereby leading to larger BDEs. 

Undeniably, the composite methods are best suited for prediction of bond dissociation enthalpies. However, these methods may be impractical for many molecules of interest. In these cases, extreme caution must be used with any other computational method. The best situation would be to test the method of choice with a series of related molecules, comparing these computed BDEs with either experimental or high level computed values to obtain some sort of correlation that would justify the use of the more moderate computational method. 

Table 6 Mean bond dissociation enthalpies (BDE) and calculated first ligand dissociation energies (FDE) of some binary metal carbonyls...

In addition, if n is not equal to 1, the total bond dissociation enthalpy. E"BDE(E ), required to convert E into E g), will have to be included. The atoms of will then need to be ionized to absorbing the... 

Thermodynamic aspects of the insertion reactions have been considered, especially with regard to reactions (b), Y = O. The enthalpy change of the reaction is related to the disruption of the metal-carbon bond, the formation of the new metal-carbon bond, the formation of the new carbon-carbon bond, and the reduction of the CO bond order. From the estimated metal-carbon bond dissociation enthalpies (BDE) of reagent and product and from the energetics of the other quantities involved in the process, the AC of reaction (g) has been calculated to be negative for R = Me or Ph and positive for R = CF3. This is in agreement with the observation that the trifluoroacetyl derivative... 

The bond dissociation enthalpy (BDE) for a diatomic molecule AB is the amount of energy necessary to bring about homolytic cleavage, that is, the enthalpy of the dissociation reaction... 

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