Charge Sharing

Of the instmments described only some are suitable for use outside the laboratory. Where any instrument is carried into a flammable environment it should either be certified as intrinsically safe for exposure to the flammable atmosphere or isolated from the atmosphere such as by keeping it within a purged enclosure. Any probe connected to the instmment must be separately considered as a possible ignition source. Electrometers are described in [ 1531. A more general review of electrostatic instruments is given in [ 136]. 

Total charge, volumetric charge density, and charge-to-mass ratio (specific charge) are useful parameters in assessing electrostatic hazards. Charge on 

This is used to measure charge, surface charge density, volumetric charge density or charge-to-mass ratio. It comprises an all-metal container, such as 

A particular problem is determination of surface charge density on a nonconductor which has charges of opposite polarity on either side (bipolar 

Electric field measurements are often performed for qualitative or comparative applications only. It is quite common to interpret electric field readings as surface potentials and instruments are available for making surface potential readings on nonconductive surfaces such as belts and 

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The carbocations formed as intermediates when allylic halides undergo Stvfl reactions have their positive charge shared by the two end carbons of the allylic system and may be attacked by nucleophiles at either site Products may be formed with the same pattern of bonds as the starting allylic halide or with allylic rearrangement... 

Carbocation more stable positive charge shared by C 3 C 5 and O... 

If hybridization is taken into account, nx can be provided only by band calculations. This is true for metals (where T inicates only the orbital) e.g. when hybridization between the f state and the (s, p, d) band is considered. In the case of cation-anion hybridization (ii.), covalency sets up. The complete charge transfer of the ionic model is reduced some charge sharing occurs between cation and anion. 

This anion, often loosely called a carbanion, is delocalised with the charge shared between the oxygen and carbon atoms. Draw arrows to show this. 

When an enolate ion is treated with an alkyl halide it results in a reaction called alkylation (Fig.E). The overall reaction involves the replacement of an a-proton with an alkyl group. The nucleophilic and electrophilic centres of the enolate ion and methyl iodide are shown (Fig.F). The enolate ion has its negative charge shared between the oxygen atom and the carbon atom because of resonance and so both of these atoms are nucleophilic centres. Iodomethane has a polar C—I bond where the iodine is a weak nucleophilic centre and the carbon is a good electrophilic centre. 

Unsaturated carbocations are also stabilized by resonance stabilization. If a pi ( 77) bond is adjacent to a carbocation, the filledp orbitals of the tt bond will overlap with the empty p orbital of the carbocation. The result is a delocalized ion, with the positive charge shared by two atoms. Resonance delocalization is particularly effective in stabilizing carbocations. 

The electronic configuration of the allyl cation (Figure 15-12) differs from that of the allyl radical it lacks the unpaired electron in tt2, which has half of its electron density on Cl and half on C3. In effect, we have removed half an electron from each of Cl and C3, while C2 remains unchanged. This MO picture is consistent with the resonance picture showing the positive charge shared by Cl and C3. 

Linker Controlled Energy and Charge Sharing Chlorophyll A Assemblies... 

However, the intermediate carbocation is stabilized by resonance, with the positive charge shared formally by three carbon atoms of the benzene ring (Scheme 2.2). The resonance hybrid structure 1 indicates the delocalization of the charge. The carbocation is also referred to as a a-complex or Whdand intermediate-... 

It was also found from laboratory studies [41], that H fCHiCNliHiO is a particularly stable cluster. This is probably due to a symmetric structure with an HiO -core having a delocalized positive charge shared by its three hydrogen atoms to each of which a CHiCN molecule is attached. 

In this diagram, the extra bond is half formed, with the charge shared between the carbon and the oxygen. 

OVERLAP OF CHARGE Shared electrons localized in Covalent bond... 

The anion in the salts A[Nb(OCH(CF3)2)g] (A = Li, Ph3C) has a single negative charge shared by 36 peripheral fluorine atoms. Consequently, it is weakly coordinating and the Li+ salt exhibits useful properties as a Lewis acid catalyst.302 Related salts of [M(OC6F5)6] are also available.303... 

The problem of the polarization of the material in response to an added charge shares the same physics with another long-standing problem [26] the calculation of linear and non-linear optical responses of mm. In fact the molecules are polarized by any electric field, being it an externally applied field or generated by a charge... 

For weak acid oxyanions that contain H atoms, such as B(OH>4, an aigument can be made to modify the shared charge definition to include the +1 charge shared by the proton with the O atom, but this has not been done in Table 4.2. 

Figure 4.6. Schematic diagram of charge sharing by the atom with oxygen in the phosphate anion.

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