  We investigate molecular evolution from a molecular cloud core to a first
hydrostatic core in three spatial dimensions. We perform a radiation
hydrodynamic simulation in order to trace fluid parcels, in which molecular
evolution is investigated, using a gas-phase and grain-surface chemical
reaction network. We derive spatial distributions of molecular abundances and
column densities in the core harboring the first core. We find that the total
of gas and ice abundances of many species in a cold era (10 K) remain unaltered
until the temperature reaches ~500 K. The gas abundances in the warm envelope
and the outer layer of the first core (T < 500 K) are mainly determined via the
sublimation of ice-mantle species. Above 500 K, the abundant molecules, such as
H2CO, start to be destroyed, and simple molecules, such as CO, H2O and N2 are
reformed. On the other hand, some molecules are effectively formed at high
temperature; carbon-chains, such as C2H2 and cyanopolyynes, are formed at the
temperature of >700 K. We also find that large organic molecules, such as CH3OH
and HCOOCH3, are associated with the first core (r < 10 AU). Although the
abundances of these molecules in the first core stage are comparable or less
than in the protostellar stage (hot corino), reflecting the lower luminosity of
the central object, their column densities in our model are comparable to the
observed values toward the prototypical hot corino, IRAS 16293-2422. We propose
that these large organic molecules can be good tracers of the first cores.
