This work reports an experimental and theoretical study of the conformational preferences of several Prelog–Djerassi lactone derivatives, to elucidate the ¹H NMR chemical shift differences in the lactonic core that are associated with the relative stereochemistry of these derivatives. The boat-like conformation of 2 explains the anomalous ¹H chemical shift between H-5a and H-5b, in which the two methyl groups (C-8 and C-9) face H-5b, leading to its higher shielding effect.