Ordering of alkane isomers by means of connectivity indices

Wiener-type indices and internal molecular energy

In earlier studies it was established that internal molecular energies (Eint) of alkanes can be reproduced, in an approximate yet reliable manner by means of a molecular-graph-based structure-descriptor U. It was also established that U is linearly correlated with the Wiener index W. We now show that the correlation between U and W is more complicated than earlier expected, and that it cannot be represented by a single line. We also show that a very good linear correlation exists between U and a modified version Wm(?) of the Wiener index, which is thus more suitable for modeling Eint than the ordinary Wiener index. .

Two theorems on connectivity indices

Two general cases are pointed out for which the ordering of molecules according to the connectivity index C(?) is the same for all values of the exponent ?.