Abstract The conformational behaviour of 10-X-substituted 1, 4-dioxa-and 1, 4, 6-trioxaspiro [4.5] decanes 1–4 has been studied by 13 C-, 19 F-and 1 H-NMR spectroscopy. Two X-ray analyses (of 2a, e) are presented, and their implications to cleavage reactions of chiral acetals are discussed. Participation of twist boat forms in the conformeric equilibrium of at least 1c has been made plausible by observing 13 C, 19 F-NMR coupling constants. The ...