Planar hexagon

If you make a molec Jr j ular model of cyclo hexane you will find Its shape to be very different from a planar hexagon We II discuss the reasons why in Chapter 3... 

The benzene ring has a fully symmetrical (Deh) planar hexagonal carbon framework. Heteroatom substitution upsets this symmetry, but except in certain special cases, as for instance the thiabenzenes , the planarity of the ring is preserved. Although it is known... 

Figure 6.8 Crystal stnicture of B13C2 showing the planar hexagonal rings connecting the B12 icosahedra. These rings are perpendicular to the C-B-C chains.

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... 

Benzene, C6H(l, is another molecule best described as a resonance hybrid. It consists of a planar hexagonal ring of six carbon atoms, each one having a hydrogen atom attached to it. One Lewis structure that contributes to the resonance hybrid is shown in (11) it is called a Kekulc structure. The structure is normally written as a line structure (see Section C), a simple hexagon with alternating single and double lines (12). 

Planar hexagonal boron layers are also found in a lower boride structure Pr5, Co2+xBg (0 < X < 1), where B and Co atoms are substituting each other to some extent. 

The planar hexagons of [114] and As [115] have the highest energies of the five valence isomers. 

FIGU RE 16.2 Geometrical isomers for MX4Y2 complexes having planar hexagonal, trigonal prism, and octahedral structures. 

Fig. 3.4-15. The planarized hexagonal aperture of five types (a)-(e) of ar-10

Fig. 3.4-16. The planarized hexagonal aperture of the ground state enantiomers (GS) and the transition state (TS) of the enantiomerization of SB9H12. ...

Fig. 3.4-19. The planarized hexagonal aperture of four ar-11 (yI) clusters [see text for an explanation of R and E (a) and (b) represent anions].

P-cellulose Cellulose soluble in 17.5% basic solution but not soluble in 8% caustic solution. Boeseken-Haworth projections Planar hexagonal rings used for simplicity instead of staggered chain forms. 

For the binary alkaline earth sihcide SiSr, two different structures have been reported. One contains one-dimensionally extended zigzag chains beside isolated Si" atoms [73]. Schafer et al. prepared a modification with the same composition, which instead contained isolated sUicide units of ten atoms. In these units, planar hexagons are substituted in the 1-, 2-, 4-, and 5-ring positions by four additional Si atoms. An isostructural compound was found for germanium as well, but showing defects in this unit in the positions 1, 2, 4, and 5. Both materials could not be obtained from stoichiometric approaches, and their formation obviously is coupled to strontium excess [69] (Fig. 3). 

Triangular (a) Planar hexagonal ring (b) Puckered hexagonal ring Figure 4 Stereochemistry of copper(l) complexes... 

Exercise 21-11 Graphite crystals consist of a network of planar hexagonal rings of carbon atoms arranged in parallel layers. The distance between the layer planes is 3.35 A and all the C-C bonds within the hexagonal network are equal to 1.421 A. 

Figure 2.9b is an end-on, side view of the cell rhombus. In the figure, are outlines of three 51268 cavities (labeled A, B, and C) are shown with the vertical borders of the rhombus at centroids of each 51268. The fourth 51268 of Figure 2.9a is aligned behind the middle 51268 cavity in Figure 2.9b. This view shows both the nonspherical nature of the 51268 cavities and their nonplanar, strained hexagonal faces in contrast to the almost planar hexagonal faces in si and sll.

This relationship between (1) diffraction by a single object and (2) diffraction by many identical objects in a lattice holds true for complex objects also. Figure 2.9 depicts diffraction by six spheres that form a planar hexagon, like the six carbons in benzene. 

Figure 2.9 A planar hexagon of spheres (left) and its diffraction pattern (right).

Example 16.1-1 Find the Bravais lattices, crystal systems, and crystallographic point groups that are consistent with a C3z axis normal to a planar hexagonal net. 

---