Benzene molecular representation

Fig. Bonding molecular orbital for benzene (b) representation of benzene to illustrate delocalisation.

The electron density distribution is a four-dimensional function (the number of elearons at a given point (x,y,z)), which is difficult to visually represent. Figures 1 and 2, respectively, show a three-dimensional isoelectronic surface of benzene and a contour plot of the elearon density p(r) in the molecular plane of benzene. Both representations show only gross features of the density. In particular, the total electron density distribution is dominated by the core electrons and appears simply as an aggregate of slightly distorted spheres... 

We will find an excitation which goes from a totally symmetric representation into a different one as a shortcut for determining the symmetry of each excited state. For benzene s point group, this totally symmetric representation is Ajg. We ll use the wavefunction coefficients section of the excited state output, along with the listing of the molecular orbitals from the population analysis ... 

Figure 20. A representation of the technique used in the mechanically controllable break junction for recording the current through a single molecule, (a) The gold wire was coated with a SAM of the molecular wires (b) and then broken, under solution (c), via extension of the piezo element under the silicon surface (see Figure 19). Evaporation of the volatile components and slow movement of the piezo downward (see Figure 19) permits one molecule to bridge the gap (d) that is shown, in expanded view, in the insert. The insert shows a benzene-1,4-dithiolate molecule between proximal gold electrodes. The thiolate is normally FI-terminated after deposition end groups denoted as X can be either FI or Au, the Au potentially arising from a previous contact/retraction event.

Fig. 3. Schematic representation of the molecular vibration of [2.2]paracyclophane, in which the benzene rings move to and fro in a concertina-like fashion with respect to each other...

O Use a molecular model set to build a model of the benzene ring. Examine your model. Does your model give an accurate representation of benzene s bonding system Explain your answer. 

Whenever there are two alternative Lewi.s structures, one alone will be an inaccurate representation of the molecular itructure. A more accurate picture will be obtained by the superposition of. the two structures into a new model, which lor benzene indicated by 3. The. superposition of two or more Lewis structures into a composite picture is called resonance. 

Figure 2-2. Spatial representation (ball-and-stick model) of benzene, with C-atoms in grey and H-atoms in white. The dotted lines between the C-atoms represent the delocalized electrons. The image on the right shows the surface area of the highest occupied molecular orbital (HOMO). Note how the 71-electrons are above and below the benzene ring.

The six overlapping p orbitals create a cyclic system of molecular orbitals. Cyclic systems of molecular orbitals differ from linear systems such as buta-1,3-diene and the allyl system. A two-dimensional cyclic system requires two-dimensional MOs, with the possibility of two distinct MOs having the same energy. We can still follow the same principles in developing a molecular orbital representation for benzene, however. 

Figure 45 (a) ORTEP view of the molecular adduct 39 35 (H-bonds are represented by thin lines), (b) ORTEP view of the inclusion complex between benzene and adduct 39 35. (c) Side view of the H-bonding network of adduct 39 35. (d) Simplified representation of the view in (c) showing the right-handed helical motif of the ribbon like H-bonded core of the assembly, (e) Single strand for H-bonded units extracted from the triple-stranded heli-cate structure in 39 35 showing left-handed helicity. (f) Stereoview of the inclusion complex between benzene and adduct 39 35 [60],... 

Figure 4. Various representations of spin-coupled orbital <)>, for benzene. Left contours in the horizontal plane 1 bohr above the molecular plane. Centre contours in a vertical mirror plane. Right a representative isosurface (3-D contour).

The arrow represents the electron transfer excitation from the HOMO of the donor to the LUMO of the acceptor, iodine. (B) Schematic diagram of the back electron transfer process which leaves the molecular iodine electronically excited. (C) Pictorial representation of the HOMO in benzene and the LUMO of iodine. Adapted from Ref [55]. 

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