may have two different labels. The first series noted b concern the phenylene and
longer analogs obtained by adding 6-membered rings to the phenylene in various
topologies. A coefficient 1 is attributed to the extracyclic atom. If the additional
benzene rings are fixed in para position, the value of the coefficients of the SOMO
decreases exponentially along the chain.
1(a,b,c)
2b
-1/4
-1/4
1/4
1
-1/2
-1/2
1/2
1
-1/2
-1/2
1/2
3b
-1/4
-1/4
1/4
1
-1/2
-1/2
1/2
-1/8
-1/8
1/8
It is interesting to note that the decrease is the same when the CH 2 group is
attached in ortho position of the polyphenyl chain. At variance, for a meta position
of this group (series c, see for instance 3c below) the SOMO is not delocalized on
the chain as the chain is attached on an atom of minor color. This is a general
property: The SOMO does not exhibit delocalization tails on fragments of the
conjugated system having an equal number of atoms of the two colors which are
connected to a minor atom. This result again is independent of the magnitude of the
hopping integrals.
1/2
3c
1
-1/2
-1/2
14 Magnetic Properties of Conjugated Hydrocarbons …
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