  With the well-established correlation between the relative stabilities of
isomers and their interstellar abundances coupled with the prevalence of
isomeric species among the interstellar molecular species, isomerization
remains a plausible formation route for isomers in the interstellar medium. The
present work reports an extensive investigation of the isomerization energies
of 246 molecular species from 65 isomeric groups using the Gaussian-4 theory
composite method with atoms ranging from 3 to 12. From the results, the high
abundances of the most stable isomers coupled with the energy sources in
interstellar medium drive the isomerization process even for barriers as high
as 67.4 kcal/mol. Specifically, the cyanides and their corresponding
isocyanides pairs appear to be effectively synthesized via this process. The
following potential interstellar molecules; CNC, NCCN, c-C5H, methylene ketene,
methyl Ketene, CH3SCH3, C5O, 1,1-ethanediol, propanoic acid, propan-2-ol, and
propanol are identified and discussed. The study further reaffirms the
importance of thermodynamics in interstellar formation processes on a larger
scale and accounts for the known isomeric species. In all the isomeric groups,
isomerization appears to be an effective route for the formation of the less
stable isomers (which are probably less abundant) from the most stable ones
that are perhaps more abundant.
