The perplexity of how the building blocks of life formed from simple and abundantly-available precursors on early earth has baffled scientific community for centuries. In order to get a clearer picture, the present study proposes and investigates plausible ammonia-assisted, free radical pathways for nucleobase formation from starting precursors such as cyanoacetaldehyde, urea, cyanoacetylene and cyanamide. Particularly, density functional theory is used to obtain optimized geometries and zero-point vibrational energy corrected electronic energies of reactants, transition states, intermediates and products along the reaction pathways in the gas phase at B3LYP/6–311G(d,p) level, as well as in the water (dielectric constant of 78.3) and ammonia (dielectric constant of 22.4) using the IEFPCM framework. Our proposed mechanisms are characterized by a smaller number of precursors and relatively lower barriers compared to previously reported reactions with other prebiotic precursors [1-3]. Features such as barrier-less formation of imidazole intermediate and favorable contribution of prebiotic enolate chemistry highlight the plausibility of the presently proposed pathways. The pathways are most suitable to environments like prebiotic earth (for purine formation) and present-day Titan (for purine and pyrimidine formation) where radical reactions are rendered feasible by continuous influx of UV and cosmic radiations. Overall, our analysis proposes kinetically accessible routes to nucleobases formation, and will hopefully contribute towards understanding the relevance of these precursors in prebiotic reactions. References: Jeilani, Y. A. Williams, P. N. Walton, S., Nguyen, M. T. (2016) Phys. Chem. Chem. Phys.,18, 20177-20188. Jeilani, Y. A. Fearce, C. and Nguyen, M. T. (2015) Phys. Chem. Chem. Phys.,17, 24294-24303. Nguyen, H. T. Jeilani, Y. A., Hung, H. M. and Nguyen, M. T. (2015) J. Phys. Chem. A, 119, 8871-8883.