The
pseudostagnation graphs of the current density induced by a
magnetic field perpendicular to the plane of the carbon atoms of benzene
and cyclopropane, chosen as archetypal of π- and σ-aromatic
molecules, have been worked out. Saddle nodes forming the saddle stagnation
lines of the pseudostagnation graph have been connected by means of
trajectories of the current density, which delimit the border of four
different sectors of flow around each saddle line. The merging of
all such boundary trajectories provides local zero-flux surfaces in
the pseudocurrent density, i.e., separatrices, which split the induced
current density field in a number of three-dimensional domains of
flow. As a result, a new partition scheme, corresponding to the physical
flow that one could observe, has been obtained. For benzene and cyclopropane,
by integration of the current density over the various spatial domains,
the parallel component of the nuclear magnetic shielding and magnetizability
tensors has been decomposed into contributions that are hard to reconcile
with any atomic models of partition.