Using 1D and 2D NMR spectra, the compounds obtained, in a mixture, in the reaction of glycerol with iodine were identified as the two isomers (cis and trans) of 2‐iodomethyl‐5‐hydroxymethyl‐1,4‐dioxane and the two isomers (cis and trans) of 2‐iodomethyl‐6‐hydroxymethyl‐1,4‐dioxane. Thus, the composition of the pharmaceutical formulation named IPG has finally been established.