AbstractQuantitative conformational data for a 4‐vinyl group in the 1, 3‐dioxane system are obtained trough a study of the conformational behaviour of both trans substituted 4‐vinyl‐6‐methyl‐1, 3‐dioxanes and cis substituted 4‐vinyl‐5‐methyl‐1, 3‐dioxanes. Some appropriate anan co meric model compounds have been prepared. The results were obtained both by a 300 MHz1H‐NMR spectroscopic study and by epimerisation studies. δG°(4‐vinyl) may