Isolobal definition

As Figure 15-2 shows, each of these fragments has a single electron in a hybrid orbital at the vacant site of the parent polyhedron. These orbitals are sufficiently similar to meet Hoffmann s isolobal definition. Using Hoffmann s symbol to designate... 

The isolobal definition may be extended to isoelectronic fragments having the same coordination number. For example,... 

Definition Two fragments are isolobal if the number, symmetry properties, approximate energy and shape of their frontier orbitals, and the number of electrons occupying them are similar - not identical, but similar. [R. Hoffmann 1982]. 

Hoffmann has called these two fragments isolobal (etymologically with the same lobe) and spread the definition. This powerful concept, well enlightened by Hoffmann, has allowed to bring closer together different types of molecular structures of both organic and inorganic chemistries. 

Obviously these isolobal comparisons can be made for any compound of boron. Systematic application of the analogy in boranes will definitely unearth a lot of new chemistry, extending the chemistry of the boranes to other systems. 

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