Lone pairs of electrons localized

As expected from the Lewis acidity of Ti4+, the titanosilicates strongly adsorb and oxidize basic nitrogen-containing compounds with a lone pair of electrons localized on the N atom. By contrast, nitrogen oxides (NOx) and nitro compounds... 

Assume that each main group element in the cluster retains a lone pair of electrons, localized outside the cluster (i.e. not involved in cluster bonding). 

In cumulene 133, the methylated pyridyl moieties can be regarded as 4-pyr-idylidene carbenes. While the redox reactivity of 133 was not directly investigated, it is known that the two-electron oxidized cation (133 ) is stable because it is the precursor to 133. Germylone 134 could also be regarded as the mesoionic germylene 134 however, this compound readily underwent double methylation, thus corroborating the existence of two lone pairs of electrons localized at the Ge center. ... 

It is notable that pyridine is activated relative to benzene and quinoline is activated relative to naphthalene, but that the reactivities of anthracene, acridine, and phenazine decrease in that order. A small activation of pyridine and quinoline is reasonable on the basis of quantum-mechanical predictions of atom localization encrgies, " whereas the unexpected decrease in reactivity from anthracene to phenazine can be best interpreted on the basis of a model for the transition state of methylation suggested by Szwarc and Binks." The coulombic repulsion between the ir-electrons of the aromatic nucleus and the p-electron of the radical should be smaller if the radical approaches the aromatic system along the nodal plane rather than perpendicular to it. This approach to a nitrogen center would be very unfavorable, however, since the lone pair of electrons of the nitrogen lies in the nodal plane and since the methyl radical is... 

Based on the requirement that repulsion should be minimized, idealized structures can be obtained based on the number of electrons surrounding the central atom. However, unshared pairs (sometimes called lone pairs) of electrons behave somewhat differently than do shared pairs. A shared pair of electrons is essentially localized in the region of space between the two atoms sharing the pair. An unshared pair of electrons is bound only to the atom on which they reside, and as a result, they are able to move more freely than a shared pair, so more space is required for an unshared pair. This has an effect on the structure of the molecule. 

The major contribution to the difference in BDEs comes rather from the second factor, i.e. the difference between the changes in hybridization that occur upon removing a hydrogen atom from NH2 and CH3 77 Loss of H from both NH2 and CH3 allows the 2s character in the remaining doubly occupied a orbitals to increase. However, the electrons in the lone pair orbital of triplet NH benefit from rehybridization more than those in the C-H bonding orbitals of triplet CH2 or, for that matter, more than the electrons in the N-H bonding orbital of triplet NH. The reason is that the lone pair of electrons in NH is localized almost entirely on N whereas, the pair of electrons in a C-H or N-H bond is shared between hydrogen and the atom to which it is bonded. 

The alternative possibility of protonation of amidines on the amino-nitrogen depends on its basicity, after its lone pair of electrons has been localized. This localization energy is not known and neither is the inductive effect of the residue attached to the amino-nitrogen in [36], but an amino-nitrogen attached to an -hybridized carbon... 

Chemically speaking there is little to say. Canonical Hartree-Fock molecular orbitals leave no place for classical chemical concepts such as bonds between atoms or groups, lone pairs, resonance hybrids, etc. However, chemists still utilize these concepts because they are extremely useful in correlating and understanding chemical facts. Even when one manages to localize the canonical molecular orbitals (which is not always straightforward) in regions such that they could be associated with lone pairs or individual chemical bonds, it is important to bear in mind that the orbitals represent localized one-electron states, and not a two-electron chemical bond between atoms or a lone pair of electrons, as will be discussed further. 

It is interesting to compare the implications expressed by these subrules with the depiction of some localized molecular orbitals in Figure 3-41 [97], The lone pair of electrons occupies more space than do the bonding pairs in the vicinity of the central atom. Also, a bond to a more electronegative ligand such as fluorine occupies less space in... 

As a prerequisite for the use of these functions a lone pair of electrons must be localized at one of the involved atoms, if a bridge is to be formed. The newly formed delocalized DE-system then comprises two bonds, four electrons and three atomic centers. The diagonal functions ensure the required electron balance. 

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