Many accounts of the origin of life assume that the spontaneous synthesis of a self-replicating nucleic acid could take place readily. Serious chemical obstacles exist, however, which make such an event extremely improbable.
Prebiotic syntheses of adenine from HCN, of D, L-ribose from adenosine, and of adenosine from adenine and D-ribose have in fact been demonstrated. However these procedures use pure starting materials, afford poor yields, and are run under conditions which are not compatible with one another.
Any nucleic acid components which are formed on the primitive earth would tend to hydrolyze by a number of pathways. Their polymerization would be inhibited by the presence of vast numbers of related substances which would react preferentially with them.
It appears likely that nucleic acids were not formed by prebiotic routes, but are later products of evolution.