tail-to-tail coupling

In chemistry, "tail-to-tail coupling" refers to a specific way atoms link together. This type of linkage is particularly observed in isoprenoids, which are organic compounds. For example, in the formation of squalene, a triterpene hydrocarbon, two smaller units are joined by a tail-to-tail bond between carbon atoms 4 and 4. This process is distinct from the more common head-to-tail coupling seen in isoprenoid biosynthesis. The mechanism of tail-to-tail coupling has been a subject of significant research, with studies by chemists like John W. Cornforth revealing complex intermediate steps involving three-membered rings.1