The Randic-Kier-Hall Molecular Connectivity Indices

The Randic-Kier-Hall Molecular Connectivity Indices 

Kier and HaU extended the definition of the 5 connectivity index in order to incorporate heteroatoms and multiple bonds in the definition of the connectivity index % [13-15]. They noticed that the 5 connectivity (atom degree) may be expressed as  

Kier and Hall used the valence 5 index from Eq. (3) to define the family of molecular connectivity indices Xt [13-15]  

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