Another set of structural parameter, which were suggested to play an important role for nonenzymatic RNA primer extension are the conformations of the key ribose rings, which were shown to correlate with the distance between the O3 ′ atom at the terminus of the primer and the P atom of the adjacent activated nucleotide . In particular, previous works suggested that high population of the C3 ′ -endo ribose conformation within the imidazole-bridged dinucleotide intermediate could facilitate efficient formation of the new phosphodiester linkage . To establish this, we measured the value of the C1 ′ -C2 ′ -C3 ′ -C4 ′ dihedral angle (see Fig. ) throughout each trajectory for which values greater than 20 • were attributed to the C3 ′ -endo arrangement and values lower than -20 • were classified as the C2 ′ -endo conformation. The relative populations collected in Fig. demonstrate that the 3 ′ -terminal nucleotide of the primer predominantly adopts the C3 ′ -endo conformation, which aligns with the canonical A-form of RNA.