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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. July 2002, Volume 1, Number 7, 360-366 |
The Structural Interpretation of the Randic Index
Ernesto Estrada
Internet Electron. J. Mol. Des. 2002, 1, 360-366
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Abstract:
The Randic index is one of the most successful molecular descriptors
in structure-property and structure-activity relationships studies. In
spite of some attempts to interpret the physical meaning of this index it
is still not clear what exactly this index measures in a molecular
structure. The finding of the structural interpretation of this topological
index will open the doors to novel applications as well as to a better
understanding of the models developed with its use. The inverse
squared-root of the vertex degree is identified here as a measure of
the relative accessible perimeter of an atom from the outside. These
perimeters, which have length units, are proposed to be measured in a
new unit called the Randic (R). One Randic correspond to the
perimeter of a carbon atom with degree one. On this basis, the bond
contributions to the Randic index are relative areas of bond
accessibility from the environment. Consequently, the Randic index is
interpreted as the relative molecular area of external accessibility, that
is the sum of relative accessibility bond areas in a molecule. The
results obtained here provide the Randic index with a clear structural
interpretation, which is very close to the physical thinking commonly
used in chemistry.
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