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Original scientific paper

Chemical Graph Theory. V. On the Classification of Topological Biradicals

Jan V. Knop ; Computer Centre, The University of Dusseldorf, 4000 Dusseldorf, Federal Republic Germany
Dejan Plavšić ; The Rugjer Boskovic Institute, P.O.B. 1016, 41001 Zagreb, Croatia, Yugoslavia
Milan Randić ; Ames Laboratory - DOE, The Iowa State University, Ames, Iowa 50011, and Department of Mathematics and Computer Science, Drake University, Des Moines, Iowa 50311, U.S.A.
Nenad Trinajstić ; The Rugjer Boskovic Institute, P.O.B. 1016, 41001 Zagreb, Croatia, Yugoslavia

Full text: english pdf 13.464 Kb

page 411-441

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We have considered skeletal forms for topological (conjugated)
biradicals and have examined alternative structural classification
schemes for them. In particular, we have looked more closely at
the classification proposed by Herndon and Ellzey, based on the
multiplicity of the zero eigenvalue and have examined all acyclic
forms having 12 or fewer carbon atoms, and all cyclic forms having
8 or fewer carbon atoms. Whlle the present work does not contribute
to resolving the controversy as to which type of biradical
can be expected to have the singlet, and which the triplet ground
state, it provides the possibility of grouping compounds of the same
expected ground state and thus allows the deduction of similar
properties for members of the same group. Hence, definitive theoretical
or experimental results obtained for a new standard species
can then be applied to a wider body of biradicals. Examination
of the distribution of »unpaired« spin density and the character
of bonds which have a constant body type (so-called essentially
single or essentially double CC bonds) provided guidance for deriving
a number of rules for the construction of larger topological
biradical forms by the combination (as fragments) of smaller-sized
biradicals or other molecular fragments.


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