Heterolytic bond

When heterolytic bond cleavage is favored, the configuration energies as functions of intemuclear distance vary as shown below. 

Configuration correlation diagram for a homonuclear case in which heterolytic bond cleavage is energetically favored. 

State correlation diagram for heteronuclear case in which both heterolytic bond cleavage products are energetically favored relative to homolytic cleavage. 

Table 1.4. Heterolytic Bond Dissociation Energies for Some C-H and C-Cl Bonds S...

Photolysis, 350 nm, CH3CN, H2O. The by-product from the reaction is 2-phenyl-benzo[ ]furan. Cleavage with TBAF and PhCH2SH has been demonstrated (70-94% yield). The related 3,5-dimethoxybenzoin analogue is cleaved with a rate constant of >10 sec Photolytic cleavage occurs by heterolytic bond dissociation. ... 

The converse of polymerization is heterolytic bond scission leading either to R3Sn+ or R3Sn species. Tricoordinate organotin(IV) cations can readily be synthesized at room temperature by hydride or halide abstraction reactions in benzene or other solvents.For example, with R = Me, Bu or Ph ... 

Reactions between cations and anions in the gas phase generally proceed with no activation energy. The simplest example is heterolytic bond dissociation. 

Heterolytic Bond Dissociation. A process in which a bond is broken and a cation and anion result. 

Heterolytic bond breakage (Section 5.2) The kind of bond-breaking that occurs in polar reactions when one fragment leaves with both of the bonding electrons A B - A+ + B . ... 

In the absence of solvation mechanisms, the process of homolytic bond scission in organic compounds requires much less energy than heterolytic bond scission... 

FIGURE 2.3. The energetics of a heterolytic bond cleavage reaction in a polar solvent. The specific example shown corresponds to the CH3OCH3— CH3 + CH30 reaction in water. The energy of the covalent state does not include the effect of the solvent on this state, but a more consistent treatment (e.g., eq. (2.21) should account for the polarization of the solvent toward the charges of the ionic state. This would result in destabilization of H31. 

In order to clarify the implementation of the LD model in VB calculations, it is useful to apply this model to the heterolytic bond cleavage of... 

Chemical reaction rate, see Rate of reaction Chemical reactions condensed phases, 42-46 enzymatic, see Enzymatic reactions gas phase, see Gas-phase reactions heterolytic bond cleavage, 46, 47, 51,... 

Heitler-London wave function, 15-16 Helium atom, wave function for, 3 Heterolytic bond cleavage, 46, 51, 47,53 Histidine, structure of, 110 Huckel approximation, 8,9,10,13 Hydrocarbons, force field parameters for, 112... 

Excited states can also decay by means of chemical reaction via heterolytic bond cleavage, leading to ions, or by homolytic bond cleavage generating free radicals. 

The results here clearly demonstrate some of the important differences between reactions in the vapor phase and those in the aqueous phase. Water solvates the ions that form and thus enhances the heterolytic bond activation processes. This leads to more significant stabilization of the charged transition and product states over the neutral reactant state. The changes that result in the overall energies and the activation barriers of particular elementary steps can also act to alter the reaction selectivity and change the mechanism. 

Comparison of zinc alkoxide and zinc hydroxide bond energies has been made. The relative heterolytic bond energies for hydroxide, methoxide, ethoxide, and tert-butoxide were determined from studies of a series of alkoxide exchange equilibria using a four-coordinate monomeric zinc tris(pyrazolyl)borate compound.335... 

Heterolytic bond dissociation (heterolysis) electronically unsymmetrical bond... 

Bromonium ion stabilities in the gas phase have also been measured in ion cyclotron resonance experiments by Beauchamp s group (Staley et al, 1977). The heterolytic bond dissociation energies shown in Table 3 are taken as a... 

With respect to the parent ethylenebromonium ion and expressed as heterolytic bond dissociation energies D (R +—Br"). Data from Staley et al. ( 1977). Calculations (Galland et al., 1990) indicate that this ion is not bridged but open. 

The next question which presents itself is whether we can explain why in some systems solvent co-catalysis occurs, whereas in others, apparently similar, it does not. Let it be said first that in fact there is very little experimental evidence on this point. From the thermochemical point of view one can say that alkyl halide co-catalysis is the more probable, the lower the heterolytic bond dissociation energy of the alkyl halide, the more stable the cation derived from the monomer, and the smaller the anion derived from the metal halide. It must, however, be remembered that the non-occurrence of alkyl halide co-catalysis may be due to a kinetic prohibition, i.e., an excessively high activation energy for a reaction which is thermodynamically possible. 

Table 1 Some heterolytic bond dissociation energies (all figures in kcal/mole) ...

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