Multiple electronic factors

Table XIII (189-199) gives details of solid-state lithium amide monomeric complexes (69)—(87). These include just three [(79), (80), and (87)] solvent-separated ion pairs. The remainder are contact-ion pairs, each with an (amido)N—Li bond. Association to dimers or higher oligomers is prevented sterically. The size of the R and/or R group in the RR N- anions can lead to monomers even when Li+ is complexed only by a single bidentate (e.g., TMEDA) or by two monodentate (e.g., THF or Et20) ligands. In such cases [(69), (71), (72), (75)-(78), and (81)—(83) ], the lithium centers are only three coordinate. Electronic factors in the anion [notably, B N multiple bonding in (75)—(78) ] also may reduce the charge density at N, and lower the ability to bridge two...

A is a reflection of electronic factors due to the added electron weakening the metal—metal multiple bond slightly and hence shifting the metal atom separation toward the high side of observed quadruple bond values, a compounding of this effect would be anticipated in the more reduced Re2 Cl4(PEt3)4 case. Such is not observed. The separation actually decreases to... 

First we have improved the re-normalization procedure by adding a constant multiplicative correction factor for the discretization error - drawn from A - and a second correction changing for each tessera and based on the value of electronic solute density (sjt) at the center of the tessera [43]. In such a way the tail error is compensated with a weight proportional to the actual value of the electronic tail at the specific site. This re-normalization procedure (called N3) is a bit more expensive than N2, but more efficient. 

Fig. 2. Electron wavefunction in a tight-binding solid (solid line). The dashed line is the multiplicative phase factor used in obtaining (437).

The regio- and stereochemistry of the Paterno-Buchi reaction depend on the structures of the reactants, on the electronic energy of the excited state carbonyl compound, and on the multiplicity of the excited state. With unsymmetrical alkenes, the products suggest preferential formation of the more substituted radical center in the biradical intermediate, but steric and electronic factors are also important. Stereoselectivities depend on the multiplicity of the excited state. For example, the reaction of excited singlet and triplet states of propanal (84) with 2,3-dihydrofuran (85) gave the diastereomers of 7-ethyl-2,6-dioxabicyclo[3.2.0]heptane (86) in different ratios (equation 12.63). ... 

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