  In this paper parent substances with molecules which can be divided into a
skeleton and six univalent substituents, and that have the properties mentioned
in the title, are considered. Two instances are the molecules of benzene and
cyclopropane. The Lunn-Senior's symmetry groups of substitution isomerism of
these compounds are described and upper bounds of the numbers of their
di-substitution and tri-substitution homogeneous derivatives are found. Lists
of the possible simple substitution reactions among di-substitution homogeneous
derivatives, on one hand, and di-substitution heterogeneous, and
tri-substitution homogeneous derivatives, on the other, are given. These
substitution reactions allow for some derivatives to be identified with their
structural formulae.
