As such, iodide is the best leaving group among the halogens, to such an extent that many organoiodine compounds turn yellow when stored over time due to decomposition into elemental iodine; as such, they are commonly used in organic synthesis, because of the easy formation and cleavage of the C–I bond. They are also significantly denser than the other organohalogen compounds thanks to the high atomic weight of iodine.
The ability of iodide to readily leave as a leaving group is what makes organoiodine compounds valuable for organic synthesis. Their yellowing due to decomposition into elemental iodine is a consequence of this property, and their higher density is also related to the heavier iodine atom.