Bonding, digonal

The most important complexes with C-donors, other than organometallics, are cyanides. AgCN has a structure with Ag—C-N-Ag bonding in linear polymeric chains it dissolves in excess KCN forming K+Ag(CN)2 (digonal with Ag-C 2.13A, i[Pg.288]

It certainly does not seem that these interactions continue in solution, so that their magnitude is weaker than solvation forces. Theoretical explanation has suggested that the unused, filled, 6s-5dz2 hybrid (section 4.1) interacts with vacant 6px,py orbitals at right angles to the digonal bonds (Figure 4.49). 

The first three geometries involve the tetrahedral, trigonal, and digonal hybrids discussed above and the fourth involves the use of pure s and p orbitals as discussed on page 149. The last structure contains three equivalent bonds at mutual angles of 60 and a fourth bond at an angle of approximately 145° to the others. U is impossible to construct s-p hybrid orbitals with angles less than 90°, and so structure V is ruled out. In this sense it may be sard that hybridization does not allow" structure V, but it may not be said that it "chooses ore of the others. Carbon hybridizes sp, sp2, and spJ in various compounds, und the choice of sp3 in methane is a result of the foot that the tetrahedral structure is the most stable possible. 

As a result of complex formation, the normally linear digonally hybridized triple bond bends to approximately 145°. Two 7i-bonds in the triple bond coordinate to two Co atoms, respectively, as shown by 130. In the following discussion, the simplified form 131 is used instead of 130 in most cases for simplicity. 

Rule 3. For digonal reaction sites (e.g. nucleophilic attacks at triple bonds), 5- to 7-exo-dig and 3- to 7-endo-dig are favored whereas 3- to 4-exo-dig reactions are disfavored. 

Thus, it is called exo , when the cyclization occurs on the inside of the unsaturated carbon-carbon bond, and it is called endo , when the cyclization occurs on the outside of the unsaturated carbon-carbon bond. Moreover, it is tet (tetrahedral 109.5°), when the carbon-carbon bond at the reaction site is sp3 hybridization it is trig (trigonal, 120°), when the unsaturated carbon-carbon bond at the reaction site is sp2 hybridization and it is dig (digonal, 180°), when the unsaturated carbon-carbon bond at the reaction site is sp hybridization. For example, there are two types of cyclization manner in 5-hexen-l-yl radical, exo-trig and endo-trig, based on the above classification. Since a 5-membered cyclopentylmethyl radical is formed through exo-trig cyclization, it is finally... 

The ring being formed has six members the breaking C=C bond is inside the new ring (endo) the C being attacked is a digonal (sp) atom (dig) >... 

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