Hydrogen-atom donors are widely used in radical reactions because hydrogen-atom abstraction is the final step in most radical chain processes. Donors can have a hydrogen atom bonded to a tin, silicon, sulfur, selenium, boron, phosphorous, or carbon atom. Most reactions involve organotin compounds, usually tri- n -butyltin hydride (Bu 3 SnH). Some organosilanes, in particular tris(tri­meth­yl­silyl) silane [(Me 3 Si) 3 SiH], are effective enough as hydrogen-atom transfers to serve as replace­ments for organotin hydrides. Most other hydrogen-atom transfers are either so reactive or so unreactive that they typically are used only in special situations.