  We look for manifestations of quantum interference effects in the Seebeck
coefficient of a molecular junction, when the electronic conductance exhibits
pronounced destructive interference features due to the presence of
quasi-degenerate electronic states which differ in their spatial symmetry. We
perform our analysis by considering three separate limits for electron
transport: coherent, fully dephased, and suffering inelastic scattering with
molecular vibrations. We find that while the conductance displays strong
signatures of the underling transport mechanisms: destructive quantum
interference features in the coherent case and thermal activation
characteristics in the inelastic limit, the Seebeck coefficient conceals
details of electron dynamics while it robustly reveals information about the
energy characteristics of the junction. We provide closed-form expressions for
the electronic conductance and the thermopower of our system as a function of
temperature, gate voltage and hybridization energy in different transport
limits, then exemplify our analysis on a specific conjugated molecule with
quasi-degenerate orbitals of different spatial symmetry.
