NMR experiments on acetals—56 : Conformational study of 1,3-dioxene

From the ¹H-NMR parameters, extracted from the spectra of 1,3-dioxene, 5-Me-1,3-diox-4-ene, 4,5-diMe-1,3-diox-4-ene and of 2,4,5-triMe-1,3-diox-4-ene, it follows that the preferred conformations are the 1,2-diplanar (sofa) C₂ form (Fig. 1B). The barrier to ring reversal in 5-Me-1,3-dioxene was found to be 7·2±0·2 kcal/mole at ?123° (in freon-21).