Electron bond-coupled

The classical VB wave function, on the other hand, is build from the atomic fragments by coupling the unpaired electrons to form a bond. In the H2 case, the two electrons are coupled into a singlet pair, properly antisymmetrized. The simplest VB description, known as a Heitler-London (HL) function, includes only the two covalent terms in the HF wave function. 

NH (X n) for which (4d) vibration of the N-H bond couples only weakly to the non-bonding 2pn orbital and for which rotation-to-electronic coupling can be dominant in causing electron ejection for high rotational levels. 

As mentioned above, the unpaired electrons of diradicals may interact with each other through bonds. The orbital phase relationships between the involved orbitals control the effectiveness of the cyclic orbital interactions underlying the through-bond coupling. 

Radical IV can be considered as a unique phosphorus radical species. Reduction of the parent macrocycle with sodium naphtalenide in THF at room temperature gave a purple solution. The FPR spectrum displayed a signal in a 1 2 1 pattern, with flp(2P)=0.38 mT. DFT calculations on radical IV models indicated a P-P distance of 2.763 A (P - P is3.256 A in the crystal structure of the parent compound and the average value of a single P-P bond is 2.2 A). According to the authors, the small coupling constant arises from the facts that the principal values of the hyperfine tensor are of opposite sign and that the a P P one electron bond results from overlap of two 3p orbitals [88]. 

The model of the chain of hydrogen atoms with a completely delocalized (metallic) type of bonding is outlined in the preceding section. Intuitively, a chemist will find this model rather unreal, as he or she expects the atoms to combine in pairs to give H2 molecules. In other words, the chain of equidistant H atoms is expected to be unstable, so it undergoes a distortion in such a way that the atoms approach each other in pairs. This process is called Peierls distortion (or strong electron-phonon coupling) in solid-state physics ... 

Note that (1) in saturated systems proton-proton couplings are seldom observed beyond three bonds, but (2) in aromatic and heterocyclic systems, four- and even five-bond coupling is commonplace. This is because spin coupling is transferred by electrons. Where you have extended conjugation, you can expect to observe coupling over a greater number of bonds. 

Fluorine can sometimes throw up some unexpected couplings in certain situations and spectra need to be handled with care Sometimes, fluorine can be seen to couple over an unfeasible number of bonds (we have seen a seven bond coupling in the past). This is because fluorine is so electron hungry that it can couple through space as well as through-bond ... 

Field electron emission coupled with flash-filament studies have been employed by Condon and Hansen to study benzene chemisorption on tungsten (21). Evidence was obtained for the chemisorption of benzene by a single bond (probably of -character) to the surface. This form of asso-ciatively adsorbed benzene [(I), Scheme 1] appeared to exist in equilibrium with cr-adsorbed-CeHs (II) and adsorbed atomic hydrogen. 

The most striking implication of the electron lattice coupling in ID chains is the appearance of the semiconducting state the equal bond ID lattice (metallic state) is unstable (33) with respect to a lattice distorsion and this so called static Peierls instability is the origin of the opening of the intrinsic band gap at the edge of the B.Z. with an infinite density of states there and the presence of band alternation. 

Joachim C (1987) Ligand-length dependence of the intramolecular electron transfer through-bond coupling parameter. Chem Phys 116 339... 

Nitrosoimines can undergo thermal reaction, a unimolecular, two-step mechanism has been proposed, as shown in Scheme 3.22 [193]. In this mechanism, a concerted electrocyclization is envisioned to form the strained four-membered ring in 41, followed by a presumably forbidden, but highly exothermic, deazetization to give 41. The electrocyclic ring closure is, at first glance, a 4-electron process, analogous to the cyclization of butadiene [194] or acrolein [194, 195]. This would be expected to involve rotation around the C=N bond coupled with C-O bond formation. 

Keywords Electron Tansfer m Energy Transfer m Through-Bond Coupling m Superexchange m Molecular Wires m Solvent-Mediated Electron Transfer m Electron Transfer in DNA m Charge Separation m Electron Transfer Through H-Bonds... 

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