Single-Bond Fragmentations

Arenesulfonyl derivatives are frequently employed in organic synthesis to activate hydroxy groups for nucleophilic substitution reactions or to protect primary and secondary amines. The PET cleavage of tosyl groups is closely related to reductions 

While most of the work related to PET reactions has been focussed on the formation of C-C bonds, the cleavage of C-O and C C bonds has also received attention. Until recently, satisfactory conditions for preparative photodeoxygenation 

A PET mechanism was postulated for this reaction, since the eleavage of the cyclobutane is not observed in the absence of triethylamine. Similarly, various cyclobutyl ketones have been cleaved under PET conditions in the presence of triethylamine [69]. 

---

Single bond fragmentations within high energy intermediates generated via PET take place almost exclusively at the radical ion stage. Although in principle... 

In contrast to radical-cations, radical-anions can be involved directly in radical reactions such as reductions, single bond fragmentations, cyclizations or tandem reactions. 

In all the alkene addition reactions we ve seen thus far, the carbon-carbon double bond has been converted into a single bond but the carbon skeleton has been left intact. There are, however, powerful oxidizing reagents that will cleave C=C bonds and produce two carbonyl-containing fragments. 

The four-membered ring of 66 [Li (dme)3] was perfectly planar with two pairs of distinctly different skeletal Ge-Ge bonds of 2.5116(6) and 2.3679(6) A the former is typical for the Ge-Ge single bonds, whereas the latter is close to the valnes of Ge=Ge double bonds. Such crystallographic features led to the formulation of the allylic-type strncture of 66 , in which the negative charge is delocalized over the Gej fragment of the four-membered ring. 

Photocatalytic C—C single-bond metathesis Cleavage of symmetrically substituted buta-diynes in combination with a subsequent alternating recombination of the fragments constitutes a C—C single-bond metathesis. 

Even-electron rule Odd-electron ions (such as molecular ions and fragment ions formed by rearrangements) may eliminate either a radical or an even-electron neutral species, but even electron ions (such as protonated molecules or fragments formed by a single bond cleavage) will not usually lose a radical to form an odd-electron cation. In other words, the successive loss of radicals is forbidden. [12]... 

Of course, a-cleavage can also occur in alicyclic ketones and other heteroatom-substituted alicyclic compounds. However, a single bond cleavage cannot release a neutral fragment, because this is still adhering to another valence of the functional group ... 

It is assumed that components of the volatilized material represent the coal mobile phase i.e., free molecules originally present in coal as well as fragments that were cleaved from macromolecules by thermal and induced scission of single bonds. 

---