Madelung reduced

Another variation of the Madelung synthesis involves use of an O-alkyl or O-silyl imidate as the C2 electrophile. The mechanistic advantage of this modification stems from avoiding competing N-deprotonation, which presumably reduces the electrophilicity of the amide group under the classical conditions. Examples of this approach to date appear to have been limited to reactants with a EW substituent at the o-alkyl group[15,16]. 

The sixth article in this collection takes up the story from where paper 4 left off. If the n + (Madelung) rule can be fully reduced, then it might rightly be claimed that the periodic table reduces fully to quantum mechanics. This is a question that has been asked in a much-quoted paper by Per-Olov Lowdin, the influential quantum chemist who for many years led the Quantum Chemistry project at the University of Florida. 

Figure 12. The Madelung sum of all die coulomb interactions of die electrolytes and their counterparts in base reduce to interactions between point charges as shown and die reaction center.

Madelung synthesis of indolesl is initiated only by strong bases at elevated temperatures. Prior deprotonation of the amide group greatly reduces the electrophilicity of the carbonyl group, and the useful scope of this synthesis is therefore limited to molecules which can survive very drastic conditions (scheme 1)... 

Figure 5.12 Reduced Madelung Energy A/d as a function of dimensionless interionic distance, for CsCl, rocksalt and zincblende crystals.

Reduced Madelung energies are converted into familiar units by specifying actual charges (integer Z), such that... 

These processes give rise to the electronic absorption bands of lowest energy observed in the pure undamaged single crystals which occur at 7.68 eV for MgO and 6.8 eV for CaO (142). Defects within the crystal structure are associated with optical absorption bands at reduced energies [for example, the anion vacancy band in the alkali halides (143)] because of the lower Madelung potential. The energy is still absorbed by the processes described in Eqs. (27) and (28), but the exciton is now bound to a defect and is equivalent to an excited electronic state of the defect. 

From a comparison of the optical absorption and excitation data for the oxides (Table V), it is clear that the energy decreases with increasing cation size along the series Mg to Ba. The bulk exciton transitions of these oxides also decrease in a similar manner (Table VI). It is possible to make a semi-quantitative calculation of the intrinsic surface energy states using the approach of Levine and Mark (151) where the ions in an ideal surface are considered to be equivalent to bulk ions except for their reduced Madelung... 

It is convenient also to generalize the Madelung constant to structures with more than one magnitude of charge (as in CaF2). This can be done for the case of a solid with formula in terms of a reduced Madelung constant (discussed, for... 

Surface excitons require less energy in their formahon than bulk excitons, owing to the reduced Madelung constant of the coordinahvely unsaturated ions at the surface [81]. 

Further insight into the stability of predominantly ionic compounds can be gained by inspection of the reduced Modelling constant. A " The reduced Madelung constant IS closely related to the derivation of the KapuslinskU equation given earlier (Chapter 4). Templeton showed that if the lattice energy a compound M, X, is formulated as ... 

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