Three-dimensional structures and projections

The approach adopted is to view the molecule in three dimensions, imagining each atom or group to be placed at a vertex of hn appropriate polyhedron. In organic chemistry this is usually the tetrahedron with carbon at the centre. Table 3.3 (p. 18) shows the polyhedra normally encountered in organic and inorganic chemistry. It also includes for each polyhedron the polyhedral symbols to denote shape and coordination number. It is to be noted that these polyhedra are often presented in a highly formalised fashion. An octahedron is often represented with the apices rather than the octahedral faces depicted, thus  

An octahedral complex, such as [Co(NH3)3(N02)3], would have an acceptor at the central position and a ligand at each of the six apices, thus  

This is not intended to indicate bonds between, for example, H3N and NO2, and it is perhaps an unfortunate hybrid of a three-dimensional representation and a line formula in which only selected bonds are shown. Care needs to be exercised when using this format, and it is not to be recommended, especially for beginning students. A more accurate and simpler representation is shown below. 

Perspective can be enhanced by shaping the bonds directed out of the plane of the paper. 

Normally, a two-electron bond is represented in these formulae by a line. When electron pairs are not conveniently localised between specific atom pairs, it is not possible to represent bonds so. For example, benzene can be represented as 

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Although the hetero ring system of fluridone and flurtamone are completely different, their three-dimensional structures and projection to a common overlay gave rise to the concept of the diaryl heterocyclic PDS inhibitors of Section 4.1.4.10 [34]. 

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