With the use of PMR the ribose conform ations have been studied in the tem perature range - 60 to + 40 °C in ND3 solutions of adenosine (A), guanosine (G), inosine (I), xanthosine (X), purineriboside (P R), 2-am inopurineriboside (2am P R), N6-isopentenyladenosine (N6ipA), 8-bromo-adenosine (8-BrA), 8-bromoguanosine (8-BrG), formycin B (F), tubercidin (T), isopropylidene-adenosine (iA), and isopropylideneguanosine (iG). The analysis is based on the two-state S ⇄ N model of the ribose m oiety proposed by Altona and Sundaralingam . The compounds studied can be classified into two groups: 1. A, I, G, X, PR , 2am PR, N6ipA, and T show a small tem perature dependence of the S ⇄ N equilibrium and [ S ] ~ 0 .6 ; 2. 8-BrA, 8-BrG, and F have a stronger tem perature dependence and [S] ~ 0 .8 . W ithin these two groups the sim ilarities observed are greater than observed in the solid state. Some therm odynam ic conclusions about the S ⇄ N and the syn ⇄ anti equilibria are presented. The results support the previously proposed correlation of the S state of the ribose with the syn conform ation of the base and of the N state of the ribose with the anti conform ation of the base. Furtherm ore, it is derived that the gg rotam er is correlated with the S state of the ribose and therefore stabilizes the syn conformation of the base.