Where Are the Lone-Pair Electrons

Where are the lone-pair electrons in subvalent fourth group compounds S. W. Ng and J. J. Zucker-man, Adv. Inorg. Chem. Radiochem., 1985, 29, 297 (178). 

Where Are the Lone-Pair Electrons in Sub valent Fourth-Group Compounds ... 

WHERE ARE THE LONE-PAIR ELECTRONS IN SUBVALENT FOURTH-GROUP COMPOUNDS ... 

Ng, S.-W., Zuckerman, J. J., Where are the Lone-Pair Electrons in Subvalent Fourth-Group Compounds , Advan. Inorg. Chem. Radiochem. 29 [1985] 297/325. 

Compare the structures of ethene and a simple compound with a C=N bond. What similarities and differences do you see between these two molecules Where are the lone pair electrons of nitrogen located ... 

FIGURE 13.5 Isosurface plots, (a) Region of negative electrostatic potential around the water molecule. (A) Region where the Laplacian of the electron density is negative. Both of these plots have been proposed as descriptors of the lone-pair electrons. This example is typical in that the shapes of these regions are similar, but the Laplacian region tends to be closer to the nucleus. 

The definition of aromaticity conceived by Hiickel strictly applies to monocyclic ring systems, but indole, constructed from the fusion of benzene and pyrrole, behaves as an aromatic compound, like quinoline and isoquinoline. The ring fusion, however, affects the properties of both components. This is reflected in the valence bond description of indole, shown in Scheme 7.1, where one canonical representation shows electron density shared between N-1 and C-3 in the pyrrole unit (implying enamine character). Note that although other canonical forms can be drawn, where the lone-pair electrons are delocalized into the benzenoid ring, their energy content is relatively high and they are of limited importance. 

Complex molecules may not possess any symmetry elements, or if they do, the localizations of the electrons can so distort the electron cloud that its symmetry bears little relation to the molecular symmetry. In such cases it may be best to revert to a description of states in terms of the individual orbitals. As an example, we will consider formaldehyde, although a molecule as simple as this is probably best described by the group-theoretical term symbol of the last paragraph. The last filled orbitals in H2CO can easily be shown to be. ..(jtco)2 (no)2, where no represents the nonbonding orbital on the O atom and the two electrons in it are the lone pair. The first unfilled orbitals in formaldehyde are the tt 0 and rr o antibonding orbitals. Promotion of one... 

There are a number of features that will be evident from the structures described herein that help illustrate the role that the inert pair of electrons plays in these structures. Some of the motifs will include the formation of polar structures where the oxoanions are aligned along one crystallographic axis, and the creation of channels to house the lone-pair electrons, which in at least one case gives rise to a chiral network. 

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