Kappa Index Values for Small Molecules

In some small molecules, certain of the P quantities may not be defined or are considered to be zero. This presents problems in applying the kappa algorithm. The calculation of a k value is possible for any molecule except those represented by a single point, i.e, methane. In general, for a straight chain molecule, k = A, and so an extrapolated value of k = 1.000 is adopted for methane. 

The calculation of values leads to nonzero values in all cases except for any graph representation of one or two atoms, such as methane and ethane. In both cases, from Eq. [52] is zero. In general, for straight chain molecules, 

In the case of values calculated from Eqs. [54] and [55], the values for methane, ethane, and propane are zero, whereas the value for butane is 4.000, 

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