Figure 23.3.2.5 

Potential plot of all furanose ring conformations. Energies are in kcal mol ⁻¹. The distance from the central point gives the maximum displacement of the out-of-plane atom from the plane of the other four. The circle is a constant-displacement trajectory chosen to pass through the potential minima on the right three-quarters of the plot. C2′-endo and C3′-endo are especially favoured, whereas O1′-exo on the left is highly disfavoured. The path from C2′-endo through C1′-exo, O1′-endo and C4′-exo to C3′-endo is a low-energy path, and many examples all along this path are known in B-DNA helices. Reprinted with permission from Levitt & Warshel (1978). Copyright (1978) American Chemical Society.