Please indulge me for one more fluorine-related post (I don’t know what’s happening to me) but I promise that I will leave the subject for a while. This is not about some late-breaking news or anything like that. It isn’t even about a paper that is particularly useful in the eyes of a modern function- and goal-oriented chemist. This work is not even new, but it is what we should all care about: it is thought-provoking. This paper was submitted to JACS by Prof. Sakurai almost 20 years ago. It details a molecule that was dubbed by the authors as a “merry-go-round” kind. You can see it in the graphic below. At first glance, its silicon NMR spectrum should contain a doublet. But it ain’t. There is a triplet and the reason for that is that the fluxional behavior around C-Si bonds leads to a unique situation in which each silicon is hexavalent, yet neutral! And then the most interesting thing happens: at higher temperatures Si NMR is actually a septet. The reason: degenerate fluorine migration (hence the name “merry-go-round”) such that each Si “sees” six fluorines at a time.
Hey – no one blogged in the days of Prof. Sakurai’s paper, so I will do it. Incidentally, this was one of the works I fell in love with while doing my PhD with Prakash and Olah. I think we can all name a few papers we remember from a while back. Some of them do leave a lasting impression.