  One of the stumbling blocks for studying the evolution of interstellar
molecules is the lack of adequate knowledge of the rate co-efficients of
various reactions which take place in the Interstellar medium and molecular
clouds. Some of the theoretical models of rate coefficients do exist in the
literature for computing abundances of the complex pre-biotic molecules. So far
these have been used to study the abundances of these molecules in space.
However, in order to obtain more accurate final compositions in these media, we
find out the rate coefficients for the formation of some of the most important
interstellar pre-biotic molecules by using quantum chemical theory. We use
these rates inside our hydro-chemical model to find out the chemical evolution
and the final abundances of the pre-biotic species during the collapsing phase
of a proto-star. We find that a significant amount of various pre-biotic
molecules could be produced during the collapsing phase of a proto-star. We
study extensively the formation these molecules via successive neutral-neutral
and radical-radical/radical-molecular reactions. We present the time evolution
of the chemical species with an emphasis on how the production of these
molecules varies with the depth of a cloud. We compare the formation of adenine
in the interstellar space using our rate-coefficients and using those obtained
from the existing theoretical models. Formation routes of the pre-biotic
molecules are found to be highly dependent on the abundances of the reactive
species and the rate coefficients involved in the reactions. Presence of grains
strongly affect the abundances of the gas phase species. We also carry out a
comparative study between different pathways available for the synthesis of
adenine, alanine, glycine and other molecules considered in our network.
