  The renormalization method is applied to investigate the electron
transmission properties of a circuit containing a benzene molecule, in which
one of the carbon atoms has been modified so as to simulate displacement in
position or replacement by another atom. Consideration of the different
possible attachments of the leads, and the relative location of the modified
atom, results in 9 distinct configurations to examine. For each configuration,
the number and locations of anti-resonances, and whether they shift upon
variation of the parameters, is seen to be the key to determining the shape of
the electron-transmission curve. In particular, those configurations, in which
the perturbed atom is not directly attached to a lead, are seen to have the
most variation in their structure, compared to pure benzene.
