Olefin , bond dissociation energies

These data appeared to be very useful for the estimation of the relative O H bond dissociation energies in hydroperoxides formed from peroxyl radicals of oxidized ethers. All reactions of the type R02 + RH (RH is hydrocarbon) are reactions of the same class (see Chapter 6). All these reactions are divided into three groups RO + R (alkane, parameter bre = 13.62 (kJ moC1)172, R02 + R2H (olefin, bre = 15.21 (kJ mob1)1 2, and R02 + R3H (akylaromatic hydrocarbon), hrc 14.32 (kJ mol )12 [71], Only one factor, namely reaction enthalpy, determines the activation energy of the reaction inside one group of reactions. Also,... 

Examination of the peak potential locations and transfer coefficient values in a series of 16 cyclic and acyclic dibromides according to the procedures detailed in Chapter 3 points to a first dissociative electron transfer rate-determining step (Scheme 4.1). It is followed by another dissociative electron transfer step, leading directly to the olefin. Intrinsic barriers for the first, rate-determining step range from 0.6 to 0.8 eV, consisting mostly of the bond dissociation contribution (one-fourth of the bond dissociation energy). 

M—H bond dissociation energies, 1, 287 photochemistry, 1, 251 single crystal neutron diffraction, 1, 578 stability toward disproportionation, 1, 301 Metal—hydrogen bonds bond dissociation energy in 1,2-dichloroethane, 1, 289 stable metal hydrides in acetonitrile, 1, 287 thermochemical cycle, 1, 286 in THF and dichloromethane, 1, 289 olefin insertion thermodynamics, 1, 629 in Zr(IV) bis-Cp complexes, 4, 878 Metal—hydrogen hydricity data, 1, 292... 

According to this interpretation, AH 24 may be identified with the cobalt-alkyl bond-dissociation energies in these compounds. However, at this stage other mechanistic interpretations, such as that involving a concerted olefin elimination, cannot be excluded (29). The investigation of these systems is continuing. 

Finally, in the context of these results, the well recognized, apparently lower thermal (and photochemical) stability of secondary cobalt-alkyls, relative to primary ones, may reflect the greater accessibility of irreversible decomposition pathways involving olefin elimination (i.e., through schemes such as that in Reactions 25-26), in addition to some probable lowering of the metal-alkyl bond-dissociation energy. 

Shono and coworkers studied the electrochemical formation of triphenylcyclopropenyl radical and its chemical behavior in the presence of hydrogen donors and olefins (Table 10). Wasielevsky and Breslow studied the reduction of various cyclopropenyl cations by second harmonic AC voltammetry (Table 11). They detected adsorption effects for some of the cations at the Pt but not at the Au electrode. The electrochemical data were used in thermodynamic sequences to evaluate the basicity of various cycloproenyl anions as well as the C-O bond dissociation energy of cyclopropenols. 

Oxygen atom transfer reactions from metal-oxo species to phosphines (forming phosphine oxides), alkylsulfides (forming sulfoxides), olefins (forming epoxides), and other substrates depend on the relative X=0 bond dissociation energies in the metal-oxo starting material and the oxidized product the reactivity scale based on bond dissociation energies was proposed.62... 

Figure 4 Plot of the d/b ratio of olefin - Pt donation and Pt - olefin back-donation against the bond dissociation energies (kcal mol" ) of compounds 1-5...

Metal—Ligand Bond Dissociation Energies in CpMn(CO)2L and Cr(CO)g(olefin) Complexes... 

Here, the term Heck-type reaction is taken to include palladium-catalyzed C-C coupling processes where vinyl or aryl derivatives are functionalized with olefins, alkynes, or organometallic reagents [see Eqs. (1) and (2)] [1]. Aryl and vinyl chlorides are most reluctant to undergo Pd-catalysed activation, as expected from the C-X bond dissociation energies [2]. 

In complex 33a, the Cr-Cr bond is strongly polarized, and the larger charge density focuses on Cr (q(C ) = —0.31e vs. q(C ) = —0.18e). The longer Co-CO bond length is calculated for CO at trans-positioned with respect to R. Therefore, it is reasonable to expect this CO ligand to dissociate more easily, as supported by the calculated bond dissociation energy of 101.3 kJ/mol. The olefin then occupies the vacant coordination site, which leads to the observed a-methylcyclopentenone. 

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