Hierarchically ordered spherical environment code

Vast tabulations of 13C chemical shift data have been assembled in computer searchable form. These databases form the basis for 13C chemical shift prediction algorithms. For the most part, carbon chemical shifts can be calculated using what is referred to as a Hierarchically Ordered Spherical Environment (HOSE) code approach [28]. To calculate a given carbon s chemical shift, the influence of each successive spherical shell is applied to the starting chemical shift for that carbon to calculate its overall chemical shift. Typically, programs will calculate shifts for 3 or 4 layers, beyond which the effects of most substituents are negligible. The spherical layers surrounding the 23-position of strychnine are shown in Fig. 10.8. 

Consider a conventional encoding of chemical structures in C-NMR spectroscopy as introduced with the so-called HOSE code (hierarchically ordered spherical description of environment). Table 7.4 contains some symbol descriptions of this code. 

Figure 7.3 Spheres around a carbon atom bold face) as the basis for encoding the structure by the hierarchically ordered spherical description of environment (HOSE) code.

The HOSE code (hierarchically ordered spherical description of environment) method was introduced by Bremser in 1978 and is widely used in commercially available spectrum prediction programs. The fundamental idea is to convert the connectivity table into a linear notation and to correlate this substructure description with the corresponding chemical shift value. 

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