Packing a punch: The 2′-hydroxy group has a strong effect on the structural and dynamic properties of RNA and DNA, and governs the hydration of the RNA minor groove. The conformation of this group was previously investigated using NOEs and ²J(C2′,OH2) and ³J(C1′/C3′/H2′,OH2) couplings at low temperature in water. In the present study, ab initio calculations were used to derive appropriate Karplus-like equations for the couplings.