Sigma cleavage

The halogen atom is far more electronegative than the carbon atom and thus attracts both electrons of the bond, which is therefore strongly polarized. The a 

FIGURE 9.24 Mechanism of allylic cleavage following ionization of a double bond. 

FIGURE 9.25 Mechanism of a cleavage from an ionized benzenic compound. 

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The two types of simple cleavages from the molecular ions in El are a (alpha) cleavage and o (sigma) cleavage. The electronegativity of the ionized atom determines the nature of the simple cleavage usually observed. 

The results can be rationalized in terms of an oxidative addition-reductive elimination mechanism as illustrated with XXII. A similar mechanism has been proposed for the acid cleavage of Pt(II)-C sigma bond (57, 58). 

Photochemical Cleavage Reactions of Benzyl-Heteroatom Sigma Bonds... 

Photochemical Cleavage Reactions of Benzyl-Heteroatom Sigma Bonds Steven A. Fleming and James A. Pincock... 

There are much fewer examples in the literature of the heterolytic cleavage of Si H bonds compared to H-H and even fewer other examples in which a cr-silane complex was observed as an intermediate in the activation. We have synthesized alkyl-substituted diimine ligands with sidearms containing labile functional groups that reserve a vacant site for binding and activation of sigma bonds as shown in Eq. (32) (108,109). 

While photochemical reactions in solids are somewhat counterintuitive and relatively rare in organic synthesis, recent examples have suggested that reactions in crystals maybe as reliable and efficient as their solution counterparts [57]. As it pertains to the photoelimination of small molecules and C—C bond-forming reactions, it is essential to recognize that product formation relies on the sequential cleavage of two sigma... 

The mass spectrum of octane is shown in Figure 15.8. The molecular ion appears at m/z 114. Cleavage of the sigma bond between C-l and C-2 would lead to the fragments shown in the following equations ... 

Cleavage of the sigma bond between C-2 and C-3 leads to the fragments shown in the following equations ... 

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