Electronic structure representation

Figure 13. Left ligand field energy-level diagram calculated for plastocyanin. Center contains energies and wavefunctions of the copper site. Energy levels determined after removing the rhombic distortions to give and C symmetries are shown in the left and right columns, respectively (from Ref. 11). Right electronic structural representation of the plastocyanin active site derived from ligand field calculations (from Ref. 11).

Fig. 18. Electronic structural representation of the plastocyanin active site. Note that the Cu-S(Met) bond is only 5° off gz, while the bonds from Cu to N(His 37), N(His 87), and S(Cys) are all less than 15° below the xy plane (from Ref. 44)...

We describe here a new structure representation which extends the valence bond concept by new bond types that account for multi-haptic and electron-deficient bonds. This representation is called Representation Architecture for Molecular Structures by Electron Systems (RAMSES) it tries to incorporate ideas from Molecular Orbital (MO) Theory [8T]. 

The advantages of spectra for structure representation are their high information content and their easy, accurate, and reproducible measurement. On top of that, spectrometers provide this spectral information already in electronic form and therefore directly amenable to further processing. 

Expand the following structural representations so as to more clearly show all the atoms and any unshared electron pairs... 

Predict the structure of the compound S2CI2 from the electron dot representation of the atoms. After you have predicted it, turn back to Figure 6-12, p. 103, and check your expectation. 

The molecule NH2 has residual, unused bonding capacity and is extremely reactive. The molecule N2H4 (hydrazine) is much more stable. Draw an electron dot representation of the bonding of hydrazine. Draw its structural formula (show which atoms are bonded to each other). 

Ethylene is a simple compound of carbon and hydrogen with the formula QH4. Thus it has two less hydrogen atoms than does ethane, QH6. This means that to write a structure of ethylene we must take account of two electrons that are not used in C—H bond formation. Suppose we write an electron dot representation involving only single bonds... 

Predict the structure of the compound N2F2 from the electron dot representation of the atoms and the molecule. 

It should also be said that the reason why Bent and Weinhold devote such attention to the n + ( rule is that, as mentioned earlier, the rule is clearly represented on the left-step table, the form of the periodic table that they favor. In addition, as was mentioned, the authors believe that the best representation of the periodic system should be based on the electronic structure of the neutral atoms of all the elements and not on their macroscopic properties. 

A methyl group may be shown in a structural representation as CH3 or Me, and similar pseudo-elemental symbols are used for ethyl, propyl and butyl side chains. It is cortrmon to represent a phenyl group as either Ph or as a hexagon with a circle irtscribed within it. This circle is meant to represent electron density that lies above and beneath the main plane of the molecule. However, when faced with... 

We can expect that in future it might probably enable us to characterize the reactivity of all reaction participants, including the reaction components and the catalyst itself, in terms of their electronic structure. The quantum chemical methods for approximate description of the polyatomic molecules (reaction components) have already been worked out. However, a very important problem arises here, one which has to be studied carefully, namely, the representation of the catalyst in the frame of this theoretical approach. 

Fig. 4 Schematic representation of (1) the energy of electron donor (D) or electron acceptor (A) units (regardless as to whether molecules or electrodes), (2) the HOMO and LUMO molecular orbitals, and (3) the energy gap AE between D/A and the molecular orbitals, (a) AE is changed by changing the electronic structure of the molecular bridge, (b) AE is changed by changing the energy levels of the donor or acceptor units...

Sections 3.3 and 3.4). The strong interactions (3.249) emphasize that the localized structural representation (3.248), although optimal, fails to depict important details of the actual electron distribution in this highly delocalized species. 

The NBO analysis reveals the strong electronic similarities between C2B9H112-and C5H5-. The optimal NBO Lewis structure representations, (3.268a)-(3.268c), all have two-center single bonds connecting the B7, Bg, B9, C10, and Cn rim atoms, with the familiar motif of a two-center B—B bond flanked by four... 

Our discussion of electronic structure has been in terms of band filling only. Of course, there is a lot more to know about band structures. The density of states represents only a highly simplified representation of the actual electronic structure, which ignores the three-dimensional structure of electron states in the crystal lattice. Angle-dependent photoemission gives information on this property of the electrons. The interested reader is referred to standard books on solid state physics [9,10] and photoemission [16,17]. The interpretation of photoemission and X-ray absorption spectra of catalysis-oriented questions, however, is usually done in terms of the electron density of states only. 

Lewis was an American scientist bom in 1875 in Massachusetts, USA. He started his academic career in 1912 and proposed the theory of electron sharing in 1916 which as we have seen is of great importance to chemists. Because of this theory, electron dot representation is also named Lewis dot structure . 

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