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.
Because iodide is the most effective leaving group among halogens, many organoiodine compounds decompose into elemental iodine over time, causing them to turn yellow. This makes them useful in organic synthesis due to their ease of breaking the C–I bond. Additionally, they are denser than other organohalogen compounds because of iodine's high atomic weight.