AN INDEX OF ELECTROTOPOLOGICAL STATE FOR ATOMS IN MOLECULES

A new method for molecular structure quantitation is described, in which both electronic and topological attributes are united. The method uses the hydrogen-suppressed skeleton to represent the structure and leads to a graph invariant index for the individual atoms and hydride groups of the molecular skeleton. An intrinsic atom value is calculated for each atom as I = (delta-v + 1)/delta, in which delta-v and delta are the counts of valence and sigma electrons of atoms in the molecular skeleton, that is, exclusive of bonds to hydrogen atoms. The electrotopological state value S(i) for an atom i is defined as S(i) = I(i) + DELTA-I(i), where the influence of atom j on atom i, DELTA-I(i), is given as SIGMA(I(i) - I(j))/r2., r is the graph separation between atoms i and j, counted as number of atoms, including i and j. The information in the electrotopological state values is revealed by examples of various types of organic structures, including chain branching and heteroatom variation. The relation of the E-state value to NMR chemical shift is demonstrated for a series of carbonyl compounds.