Our study shows that several hypotheses regarding HCN's reactions to molecules and polymers can be ruled out on the grounds of thermodynamics. For example, diaminomaleonitrile (5), a prominently suggested reaction intermediate in HCN-based prebiotic chemistry, is predicted to be lower in energy compared to many proposed polymer products. Our study also infers a new perspective on adenine (7), a nucleobase, present in all life as we currently know it (Fig. ).