Ordering of alkane isomers by means of connectivity indices

Abstract

The connectivity index of an organic molecule whose molecular graph is G is defined as C(l) = S(dudu)1, where du is the degree of the vertex u in G, where the summation goes over all pairs of adjacent vertices of G and where l is a pertinently chosen exponent. The usual value of l is –1/2, in which case c = C(–1/2) is referred to as the Randic index. The ordering of isomeric alkanes according to c follows the extent of branching of the carbon-atom skeleton. We now study the ordering of the constitutional isomers of alkanes with 6 through 10 carbon atoms with respect to C( l) for various values of the parameter l. This ordering significantly depends on l. The difference between the orderings with respect to c and with respect to C( l) is measured by a function D and the l-dependence of D was established.

Keywords

• connectivity index
• Randic index
• alkanes
• isomer ordering