Ring-current effects in the nmr of nucleic acids: A graphical approach

The spatial dependence of the ring‐current magnetic anisotropy of nucleic acid bases is presented in a series of graphs in cylindrical coordinates. The curves may be used to calculate the ring‐current shift at a point in a cylinder of radius 10Å extending 8 Å above and below each ring of the base. These distance effects are found to influence considerably the predicted chemical shifts of nucleic acid protons, particularly in RNA duplexes. The contribution of polarization (electric field) effects and the diamagnetic anisotropy of individual atoms (local Δχ) are briefly discussed.