7i bonding

Organic chemists usually think of a double bond as the combination of a a bond and a 7i bond. An alternative is to consider a double bond as made up of two equivalent bent bonds (these bonds point above and below the intemuclear axis). 

HOMO of dimethylsulfonium ylide describes the extent to which a 7i bond is present. 

Bismuth ligands, 2,989-1061 bonding, 2,1030-1041 7i bonding, 2, 1033-1039 trigonal bipyramidal complexes, 2,1036 Bismuth line, 3,294 Bismuthotungstates, 3, 1042 Bismuth pentafluoride, 3, 292 Bismuth tribromide, 3, 291 Bismuth trichloride, 3, 290 Bismuth trifiuoride, 3, 290 Bismuth triiodide, 3,292 Bismuth trioxide, 3,284 2,2 -Bisphenol metal complexes color photography, 6,109 Bis(trimethylene)triamine metal complexes, 2, 49 4,4 -Bi-l, 2,4-triazolyl metal complexes, 2, 89 polymers... 

One 7i-bond of an aromatic ring can be converted to a cyclohexadiene 1,2-diol by reaction with enzymes associated with P. putida A variety of substituted aromatic compounds can be oxidized, including bromobenzene, chlorobenzene, " and toluene. In these latter cases, introduction of the hydroxyl groups generates a chiral molecule that can be used as a template for asymmetric syntheses. " ... 

The barriers for the rotation around the SS bond have been estimated from microwave data [40] and ab initio MO calculations [41, 42] as 34-36 kj mor (cis-barrier) and 24-25 kJ mol (trans-barrier), respectively. They are explained as the result of three effects First, the repulsion of the two 3p lone pairs at the sulfur atoms is lowest for r=90°. Second, the 3p lone pair electrons are partly delocalized into the antibonding a orbitals of the SH bonds originating from the neighboring sulfur atom. This hyperconjugation or 7i bond is at its maximum for r=90° but disappears for r=0° and 180°. Third,... 

The product of bis-coordination, 20 at phosphorus, could be also achieved utilizing the more nucleophilic p-dimethylamino pyridine (DMAP) [57, 58]. As shown in Scheme 12,bis-coordination of the two donors occurs in general by taking up the two orthogonal positions of the PN 7i-bonds [58]. 

A brief history of (3p-2p)7i bonds between phosphorus and carbon followed by an introduction to the methods of phosphaalkene synthesis that are pertinent to this review will be provided. The earliest stable compound exhibiting (3p-2p)7x bonding between phosphorus and carbon was the phosphamethine cyanine cation (1) [33]. An isolable substituted phosphabenzene (2) appeared just two years later [34]. The parent phosphabenzene (3) was later reported in 1971 [35]. These were remarkable achievements and, collectively, they played an important role in the downfall of the long held double bond rule . The electronic delocalization of the phosphorus-carbon multiple bond in 1-3, which gives rise to their stability, unfortunately prevented a thorough study of the chemistry and reactivity of the P=C bond. 

The double bond in ethylene contains one a bond and one 7r bond. The a bond forms from the end-on overlap of two hybrid orbitals, and the 7i bond forms from the side-by-side overlap of two atomic p orbitals. Figure 10-21 shows the complete orbital picture of the bonding in ethylene. Ethylene is the simplest of a class of molecules, the alkenes, all of which contain CDC double bonds. The alkenes are the subject of our Box on page 404. 

By contrast, addition-elimination mechanisms in their simplest form begin with formation of an addition complex resulting from a well on the PES, followed by dissociation of the complex, yielding products. Both the entrance to and exit from the well may be hindered by barriers on the PES. Addition mechanisms are uncommon in radical -b saturated closed-shell reactions due to the difficulty of bond formation with the saturated species (ion-molecule reactions are exceptions). By contrast, additions are more common in radical -b unsaturated closed-shell species, where the double or triple bond allows a low barrier or barrierless pathway for addition of the radical into the 7i-bond of the stable species, such as the reaction... 

These d indices for cations and anions relevant to AB cements are shown in Table 2.5. Bases which add on through F or O and do not form i-bonds have similar hardness values they are hard bases. Soft bases form dative 7i-bonds with many cations. They have high-energy-level occupied orbitals with unshared electron pairs. 

In general, transition metal-catalyzed hydroaluminations of alkynes occur in a syn fashion, i.e., both aluminum and hydride are added to the same face of the 7i-bond. Isomerization of the initially formed vinylalane is usually not observed under the mild reaction conditions used for these transformations. 

The carbon-carbon triple bond consists of two 7i bonds and one a bond. 

A lithium atom donates an electron to The radical anion acts as the 7i bond of the alkyne. An electron a base and removes a... 

The 7i bond is formed by overlap of the carbon p orbital with a p orbital from the oxygen atom. 

The 7i bonding molecular orbital of formaldehyde (HCHO). The electron pair of the n bond occupies both lobes. 

X-Ray crystallography has been commonly used to confirm structures of new 1,2,5-oxadiazoles. X-ray data show that the heterocyclic ring is planar with C2v symmetry. The delocalization of 7i-bonds depends on the C-substituents. 

Summarizing the available bonding information, decamethylsilicocene (1) is regarded as an electron-rich silicon(II) compound containing a hypercoordinated silicon atom which is sandwiched between two rather weakly 7i-bonded pentamethylcyclopentadienyl ligands and thus is effectively shielded the lone-pair orbital at silicon is part of the frontier orbitals of the molecule. 

The 7i-bond is spread out evenly over the three S—O linkages. This leads to an average bond order of 1.33 for the three S—O bonds in SO3. By following this "combined approach , we end up with a structure that has the a-bond framework sandwiched between the delocalized 71-molecular orbital framework ... 

Once a particular 6-membered ring is selected as a site for applying the Diels-Alder transform, six possible [4 + 2] disconnections can be examined, i.e. there are six possible locations of the 7i-bond of the basic Diels-Alder retron. With ring numbering as shown in 36, and... 

A more general approach involves development of reagent-controlled catalysts for X+-transfer, defined as having a chiral reagent that directs the addition of the electrophilic X+ to one face of the 7i-bond, but only a limited number of reports of these exists (17,18,19,20) including our own work (21,22,23). In one completed study (21) we investigated the transfer of Br+ from... 

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