ON TOPOLOGICAL INDICES INDICATING BRANCHING
PART I. THE PRINCIPAL COMPONENT ANALYSIS OF ALKANE PROPERTIES AND INDICES

A. Perdih*, M. Perdih
Mala vas 12, SI-1000 Ljubljana, Slovenia
 

ABSTRACT

The suitability of topological indices J, W, Z, D, MTI, Xu, ID, c, ll1, EAmax, and l1 as branching indices, as well as of physicochemical properties MON, BP, d, Vi, Vm, Vc, Tc, Pc, dc, Zc, ac, DHv, A, B, C, nD, MR, a0, b0, DHfg, DGfg, S, R2, and w, as reference properties for the branching of alkanes is tested by means of the Principal Component Analysis (PCA). On the PCA plots, alkanes are separated by several criteria in the following descending order of importance: carbon number, number of branches, whether the carbons are tertiary or quaternary, the position of branches, the shape and symmetry of molecules. Most properties and indices correlate highly with the carbon number of alkanes and the influence of branching on them is much lower. MON (motor octane number) depends first of all on the number of CH2 groups. The properties are divided into intrinsic and interaction-dependent ones. It is explained why the latter ones are less suitable as primary references for branching. Two definitions of branching are presented, the Methane-based definition as a general definition and the n-Alkane-based definition as a special definition more familiar to chemists.