Benzene model structure

Scheme 10.4 (a) Structural changes in the Re-CVD/HZSM-5 (19) catalyst during direct phenol synthesis from benzene and O2 and treatment with NH3 (b) proposed model structure of the N-interstitial Reio-cluster catalyst supported in the pore of HZSM-5 (calculated by DFT). 

A true picture of benzene s structure was not determined until the 1930s when Linus Pauling produced his work on the chemical bond. Benzene does not exist as either of its resonance structures, and its structure should not be considered as either one or the other. A more appropriate model is to consider the... 

Assuming the C-C bonds of the prism all are the same length, determine how many mono-, dr-, and tribromine-substituted isomers are possible for 17. Compare the results with those expected for benzene with structure 13. If you have molecular models of the ball-and-stick type, these will be very helpful. A simple alternative model for 17 would be a piece of stiff paper folded and fastened as in 18 to give a prism with three equal square faces. 

Computational studies on the n-n stacking problem began with the simplest model the benzene dimer. While not the only possible configurations, the benzene dimer structures most studied are the sandwiches 77s (D f) and 77s (T>6 ), the parallel displaced 77pd, and the T-shaped configurations 77t and 77t. ... 

A special class of cyclic unsaturated hydrocarbons is known as the aromatic hydrocarbons. The simplest of these is benzene (C6H6), which has a planar ring structure, as shown in Fig. 22.11(a). In the localized electron model of the bonding in benzene, resonance structures of the type shown in Fig. 22.11(b) are used to account for the known equivalence of all the carbon-carbon bonds. But as we discussed in Section 14.5, the best description of the benzene molecule assumes that sp2 hybrid orbitals on each carbon are used to form the C—C and C—H a bonds, while the remaining 2p orbital on each carbon is used to form 77 molecular orbitals. The delocalization of these 1r electrons is usually indicated by a circle inside the ring [Fig. 22.11(c)]. 

Fig. 7.21 Model structure of benzene interacting with a single nickel atom located below the centre of the benzene ring. The two extra internal coordinates, in addition to those of benzene, are the C-Ni bond and the HCNi angle.

Ibach and Rowe found the reconstructed surface structures to be very stable to hydrogen adsorption, in that on 111 7x7 and 100 2 x 1 surfaces, no change in LEED patterns occurred up to saturation coverage. The favoured interpretation was based on the model of clean surface reconstruction proposed by Lander [76] and extended by Phillips [202], whereby surface vacancies produce warped benzene ring structures in the first and second surface layers, and such distortions are too large to be removed by hydrogen adsorption. The 111 2 x 1 structure was found to be somewhat less stable, however, and the fractional order spots disappeared on hydrogen adsorption. This was related to the Haneman clean... 

What feature(s) of the Lewis structure of benzene. Model 1, is inconsistent with the calculated C-C bond orders in Model 1 ... 

Based on the results presented above, we have performed preliminary simulations on the catalytic reaction. For this purpose, we have studied the adsorption of benzene on Raney-Nickel using one of the model structures generated as discussed... 

Figure 1. Model structures for the aromatic and nonaromatic forms of benzene...

Such images provide impressive support for the model of the benzene ring structure that had been drawn from so many different threads of evidence. 

The vibronic coupling model has been applied to a number of molecular systems, and used to evaluate the behavior of wavepackets over coupled surfaces [191]. Recent examples are the radical cation of allene [192,193], and benzene [194] (for further examples see references cited therein). It has also been used to explain the lack of structure in the S2 band of the pyrazine absoiption spectrum [109,173,174,195], and recently to study the photoisomerization of retina] [196],... 

The results of the derivation (which is reproduced in Appendix A) are summarized in Figure 7. This figure applies to both reactive and resonance stabilized (such as benzene) systems. The compounds A and B are the reactant and product in a pericyclic reaction, or the two equivalent Kekule structures in an aromatic system. The parameter t, is the reaction coordinate in a pericyclic reaction or the coordinate interchanging two Kekule structures in aromatic (and antiaromatic) systems. The avoided crossing model [26-28] predicts that the two eigenfunctions of the two-state system may be fomred by in-phase and out-of-phase combinations of the noninteracting basic states A) and B). State A) differs from B) by the spin-pairing scheme. 

Hiickel models of molecular electronic structure enjoyed many years of popularity, particularly the r-electron variants. Authors sought to extract the last possible amount of information from these models, perhaps because nothing more refined was technically feasible at the time. Thus, for example, the inductive effect was studied. The inductive effect is a key concept in organic chemistry a group R should show a - -1 or a —I effect (according to the nature of the group R) when it is substituted into a benzene ring. 

As pointed out in Chapter 7, the atomic orbital (valence bond) model regards benzene as a resonance hybrid of the two structures... 

In these line-angle formulas it is understood that there is a carbon atom at each vertex of the hexagon hydrogen atoms are not shown. This model is consistent with many of the properties of benzene. The molecule is a planar hexagon with bond angles of 120°. The hybridization of each carbon is sp2. However, this structure is misleading in one respect Chemically, benzene does not behave as if double bonds were present... 

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