The1H and13C NMR spectra of ethylidene derivatives of simple diols and of carbohydrates were measured to determine whether NMR parameters could be found which could be related to structure. Four NMR parameters were considered; the chemical shifts of the acetal proton and carbon, the2JC,Hvalue between the acetal proton and methyl carbon and the1JC,Hvalue of the acetal carbon. The values,.of these parameters were all somewhat related to ring-size; the2JC,Hvalue was most closely related. The sign of2JC,Hwas shown to be positive for 2-methy l-l,3-dioxolane and Z-methy l-l,3-dioxane by means of selective population transfer experiments. Comparison of the13C NMR chemical shifts of the acetal with the parent diol was found to give information about acetal location.