kappa2_index#

skfp.descriptors.kappa2_index(mol: Mol) → float#

Second Kappa shape index (K2).

Computes the second kappa shape index [1], which measures molecular shape based on paths of length 2. It is given by the equation:

\[K_2 = \frac{(A + \alpha - 1) (A + \alpha - 2)^2}{P_2^2}\]

where:

  • A is the number of heavy atoms

  • α is the Hall-Kier alpha index

  • P2 is the number of paths of length 2

This index captures molecular branching and shape characteristics.

Parameters:

mol (RDKit Mol object) – The molecule for which the second Kappa shape index is calculated.

References

Examples

>>> from rdkit.Chem import MolFromSmiles
>>> from skfp.descriptors import kappa2_index
>>> mol = MolFromSmiles("C1=CC=CC=C1")  # Benzene
>>> kappa2_index(mol)
1.6057694396735218
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