Homolytic bond Definition

From the above studies, it is evident that the effect of an oxidation state change on the M-H homolytic bond strength is far from being clear, and results obtained on a specific system may not lend themselves to extrapolation or generalization. Further investigations on this deceptively simple chemical bonding topic are most definitely necessary. 

The potential energy curves of a neutral molecule AB and the potential ionic products from Eqs. 7.22-7.24 are compared below (Fig. 7.13). These graphs reveal that the formation of negative molecular ions, AB"", is energetically more favorable than homolytic bond dissociation of AB and that the AB ions have internal energies close to the activation energy for dissociation [72,74,84]. The negative molecular ions from EC are therefore definitely less excited than their positive counterparts from 70-eV El. 

The material is arranged as follows. Photochemical reactions are discussed first (Section VI,A) as they represent the most thoroughly studied and only definitely established examples of the simplest type of reaction, viz., the homolytic fission of the Co—C bond. Thermal (i.e., nonphotochemical)... 

The separate and quantitative evaluation of accelerating steric effects on the homolytic cleavage of C—C-bonds allowed the definition of intrinsic barriers for the bond dissociation reaction, i.e. AG or AH at Hs = 0 in Fig. 2 or 3 or in Eq. (1-11) in general. AH is equal to or slightly than the corresponding bond dissociation energy (BDE) 6a-811 as pointed out earlier. 

Photogeneration of MnRe(CO)io from irradiation of both Mn2(CO)io and Re2(CO)io also occurs, and such cross-coupling has become a definitive test of whether homolytic metal-metal bond cleavage occurs. Kinetics of recovery of ground state Mn2(CO)io absorption after flash irradiations are consistent with formation of Mn(CO)5 radicals from the excitation (13). 

The RSE is calculated here as the difference between the homolytic C-C bond dissociation energy in ethane (5) and a symmetric hydrocarbon 6 resulting from dimerization of the substituted radical 2. By definition the C-C bonds cleaved in this process are unpolarized and, baring some strongly repulsive steric effects in symmetric dimer 6, the complications in the interpretation of substituent effects are thus avoided. Since two substituted radicals are formed in the process, the reaction enthalpy for the process shown in Equation 5.5 contains the substituent effect on radical stability twice. The actual RSE value is therefore only half of the reaction enthalpy for reaction 5.5 as expressed in Equation 5.6. 

A definite proof that no homolytic cleavage of the M-M bond is involved was obtained on the Re2 carbonyls ... 

On the other hand, as shown by the left-hand side of eqn (8.18), Katrp depends upon the relative values of the C-X and Cu X dissociation energies, in other words to Kbh and Knaio (Knaio is, as seen from its definition in Figure 8.6, the inverse of the Cu -X bond dissociation energy). The lower than expected difference between Katrp(RCI) and KATRp(RBr), based solely on the ease of homolytic cleavage (Kbh) of C-X bonds, can be explained also by the greater stability of the Cu -Cl compared to Cu -Br bond, i.e., higher chloro-than bromophilicity of Cu complexes. ... 

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