  Since the concepts for the implementation of data storage and logic gates
used in conventional electronics cannot be simply downscaled to the level of
single molecule devices, new architectural paradigms are needed, where quantum
interference (QI) effects are likely to provide an useful starting point. In
order to be able to use QI for design purposes in single molecule electronics,
the relation between their occurrence and molecular structure has to be
understood at such a level that simple guidelines for electrical engineering
can be established. We made a big step towards this aim by developing a
graphical scheme that allows for the prediction of the occurrence or absence of
QI induced minima in the transmission function and the derivation of this
method will form the center piece of this review article. In addition the
possible usefulness of QI effects for thermoelectric devices is addressed,
where the peak shape around a transmission minimum is of crucial importance and
different rules for selecting suitable molecules have to be found.
