  We study the formation and evolution of several molecules in a collapsing
interstellar cloud using a reasonably large reaction network containing more
then four hundred atomic and molecular species. We employ a time dependent,
spherically symmetric, hydrodynamics code to follow the hydrodynamic and
chemical evolution of the collapsing cloud. The flow is assumed to be
self-gravitating. We use two models to study the hydrodynamic evolution: in the
first model, we inject matter into an initially low density region and in the
second model, we start with a constant density cloud and let it collapse due to
self-gravity. We study the evolution of the central core for both the cases. We
include the grain chemistry to compute the formation of molecular hydrogen and
carried out the effect of gas and grain chemistry at each time step. We follow
the collapse for more than $10^{14}$s (about 3 million years) and present the
time evolution of the globally averaged abundances of various simple but
biologically important molecules, such as glycine, alanine etc. We compare our
results with those obtained from observations found that for lighter molecules
the agreement is generally very good. For complex molecules we tend to under
predict the abundances. This indicates that other pathways could be present to
form these molecules or more accurate reaction rates were needed.
  Keywords: hydrodynamics; star formation; ISM; chemical evolution
