Electrons localized delocalization

Sumar I, Cook R, Ayers PW, Matta CF (2015) AIMLDM a program to generate and analyze electron localization-delocalization matrices (LDMs). Comput Theor Chem 1070 55-67... 

Examine the geometry of the most stable radical. Is the bonding in the aromatic ring fuUy delocalized (compare to model alpha-tocopherol), or is it localized Also, examine the spin density surface of the most stable radical. Is the unpaired electron localized on the carbon (oxygen) where bond cleavage occurred, or is it delocalized Draw all of the resonance contributors necessary for a full description of the radical s geometry and electronic structure. 

The process is exothermic, suggesting that the phenoxy radical is particularly stable. Display the spin density surface for phenoxy radical. Is the unpaired electron localized or delocalized over several centers Is the unpaired electron in the a or 7t system Draw appropriate Lewis structures that account for your data. 

Examine the spin density surface for BHT radical. Is the unpaired electron localized or delocalized Examine BHT radical as a space-filling model. What effect do the bulky tert-butyl groups have on the chemistry of the species (Hint BHT radical does not readily add to alkenes or abstract hydrogens from other molecules.)... 

In molecular orbital terms, the stability of the allyl radical is due to the fact that the unpaired electron is delocalized, or spread out, over an extended 7T orbital network rather than localized at only one site, as shown by the computer-generated MO in Fig 10.3. This delocalization is particularly apparent in the so-called spin density surface in Figure 10.4, which shows the calculated location, of the unpaired electron. The two terminal carbons share the unpaired electron equally. 

In molecular orbital theory, electrons occupy orbitals called molecular orbitals that spread throughout the entire molecule. In other words, whereas in the Lewis and valence-bond models of molecular structure the electrons are localized on atoms or between pairs of atoms, in molecular orbital theory all valence electrons are delocalized over the whole molecule, not confined to individual bonds. 

The electrons occupy the in-phase combined orbital after the interaction. They are distribnted not only in the orbital occnpied prior to the interaction, bnt also in the overlap region and the orbital vacant prior to the interaction. The electrons localized in the occupied orbital before the interaction delocalize to the overlap region and the vacant orbital after the interaction (Scheme 13). 

Cyclopentadienylidene (10) has an even longer history than cyclopropenyli-dene (2).14 Carbene 10 possesses a triplet ground state. Its ESR spectrum indicates a structure with C2V symmetry. One electron is localized at the car-benic center, the other unpaired electron is delocalized over the five-membered ring (structure T-IO ).30 The IR and UV spectra of 10 are also known.31... 

In a similar fashion the bonding in H2 might be formally regarded as a complementary pair of one-electron donor-acceptor interactions, one in the ot (spin up ) and the other in the 3 (spin down ) spin set.8 In the long-range diradical or spin-polarized portion of the potential-energy curve, the electrons of ot and (3 spin are localized on opposite atoms (say, at on HA and 3 on HB), in accordance with the asymptotic dissociation into neutral atoms. However as R diminishes, the ot electron begins to delocalize into the vacant lsB(a) spin-orbital on HB, while (3 simultaneously delocalizes into Isa on HA, until the ot and (3 occupancies on each atom become equalized near R = 1.4 A, as shown in Fig. 3.3. These one-electron delocalizations are formally very similar to the two-electron ( dative ) delocalizations discussed in Chapter 2, and they culminate as before (cf. Fig. 2.9) in an ionic-covalent transition to a completely delocalized two-center spin distribution at... 

When the combined system of adatom and substrate is in its ground state, so that the lowest energy levels are each doubly occupied with an a- and a /2-spin electron, then, if two electrons are in a localized level, a localized surface bond will be formed. However, if the localized level is unoccupied, then an adbond formation will be achieved without localization of the bonding electrons (i.e., only delocalized electrons will be involved in the adbond). In the case of electron localization, the type of adbond is determined by the charge order of the adatom state, namely,... 

In a pericyclic reaction, the electron density is spread among the bonds involved in the rearrangement (the reason for aromatic TSs). On the other hand, pseudopericyclic reactions are characterized by electron accumulations and depletions on different atoms. Hence, the electron distributions in the TSs are not uniform for the bonds involved in the rearrangement. Recently some of us [121,122] showed that since the electron localization function (ELF), which measures the excess of kinetic energy density due to the Pauli repulsion, accounts for the electron distribution, we could expect connected (delocalized) pictures of bonds in pericyclic reactions, while pseudopericyclic reactions would give rise to disconnected (localized) pictures. Thus, ELF proves to be a valuable tool to differentiate between both reaction mechanisms. 

The Ptm-Ptm bond in the alkyl complexes exhibits a unique character in that the Pt atom acts both as Ptn and PtIV or the intermediate through electron localization and delocalization along the Pt-Pt axis (1) coordination of olefin is a Pt11 character, since no olefin-Pt17 complex is known and (2) the very easy and rapid nucleophilic attack on the coordinated alkyl ce-carbon atoms is a PtIV character. Alkyl-Ptn complexes do not easily undergo nucleophilic attack unless the com-... 

The reason for this becomes apparent when one compares the shapes of the localized it orbitals with that of the ethylene 7r orbital. All of the former have a positive lobe which extends over at least three atoms. In contrast, the ethylene orbital is strictly limited to two atoms, i.e., the ethylene 7r orbital is considerably more localized than even the maximally localized orbitals occurring in the aromatic systems. This, then, is the origin of the theoretical resonance energy the additional stabilization that is found in aromatic conjugated systems arises from the fact that even the maximally localized it orbitals are still more delocalized than the ethylene orbital. The localized description permits us therefore to be more precise and suggests that resonance stabilization in aromatic molecules be ascribed to a "local delocalization of each localized orbital. One infers that it electrons are more delocalized than a electrons because only half as many orbitals cover the same available space. It is also noteworthy that localized it orbitals situated on joint atoms (n 2, it23, ir l4, n22 ) contribute more stabilization than those located on non-joint atoms, i.e. the joint provides more paths for local delocalization. 

For the elements highlighted by the diagonal strip there is an indication that the / and d electrons may be balanced between being localized and itinerant. According to Smith and Kmetko (1983), materials close to this localization-delocalization transition can have their properties modified appreciably by small... 

This has been developed since 1986. The title letters stand for Localized Delocalized Response. The localized effect is Charton s preferred name for the inductive effect and delocalized effect is his preferred name for the resonance effect. Indeed, he would like to change the usual symbols from <7/ to 0/, and or to op for the purposes of the Extended Hammett (EH or LD) equation109. The response referred to is that of the substituent to the electronic demand of the site (i.e. reaction site in the correlation analysis of reactivity). Thus this equation, like the PSP equation, is concerned with the parametrization of substituent polarizability. 

There is, however, an exception in an infinite homogeneous electron gas, electrons are delocalized. Neglecting their orbital motion does not contradict quantum mechanics, and lacking localization is unproblematic when only cross... 

The anion-radicals depicted in Scheme 3.62 were investigated by ESR and electron adsorption spectroscopy (Gregorius et al. 1992). The para isomer appears to behave completely different from the meta isomer. In full agreement with the results from MO theoretical calculations, the unpaired electron is delocalized over the whole para isomer, but confined to a stilbene unit in the meta isomer. The remaining parts in the meta isomer are uncharged. This spontaneous charge localization is not a consequence of steric hindrance, but follows from the role of the m-phenylene unit as a conjuga-tional barrier. 

The product of desorption in all the cases considered is a neutral particle C. As r increases, i.e., as particle C moves away from the surface, the level A in Fig. 10 can be shown 2) to approach the conduction band and to merge with it in the limit r = oo at the same time the level D in Fig. 10 descends to the valence band and merges with it at r = w. In other words, an electron localized on an acceptor level A (making an n bond) or a hole localized on a donor level D (making a p bond) becomes delocalized as r increases and in the limit (at r = ) returns to the conduction band or, respectively, to the valence band, that is, becomes again one of the free electrons or holes. 

The pi-electrons cire delocalized over the entire ring structure, not localized between two carbons. This contributes to the observed stability of benzene. 

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