We study the evolution of molecular abundances in contracting
prestellar cores, including both dynamical and non-equilibrium
chemical processes.  We model both non-magnetic and magnetic cores and
explore the competing effects of various model parameters in the
evolving molecular abundances.  We find that different models show
their largest quantitative differences at the center of the core,
whereas the outer layers, which evolve much slower, have abundances
which do not differentiate between dynamical models.  Because even the
highest spatial resolution observations include contributions from
outer layers, we propose using particular abundance ratios, which have
the maximal potential for discrimination between different dynamical
models and which potentially could be used to determine molecular core
ages.