Here is something we do not hear a whole lot about: immolation of atoms during synthesis. This happens when an atom literally disappears into thin air. Once a sigma bond that used to connect that atom to its neighbor is gone, a cationic center is installed. I am not talking about your classic Sn1 chemistry, by the way, as there are no remnants of any leaving group in solution. The leaving group just valishes. If you think this is some kind of gibberish, I can tell you that I am describing quite a nice way to synthesize carbocations and later trap them with nucleophiles. The link below takes you to an old review by Speranza in which he talks about this process.

http://pubs.acs.org/doi/pdf/10.1021/cr00024a010

The reaction amounts to radioactive beta-decay that is accompanied by helium release. By the way, this remarkably effective and barrierless C-H activation (well, it is C-T activation, I suppose) is catalyst-free as well. You are probably noticing that I have paid a tribute to those practitioners of synthetic methodology who, for reasons unbeknownst to me, continue to “beat the drums” as they free reactions of some key components. I salute them all here by giving them a reminder of leaving group-free Sn1 reactions. I suppose that the only thing that would have made it more appealing from their perspective is if the reaction above had been “green”. But, alas, folks are happy with neither beta-decay nor tritiation.