The diazo-coupling reaction dates back to the 1850s (and a close association with Imperial College via the first professor of chemistry there, August von Hofmann) and its mechanism was much studied in the heyday of physical organic chemistry.[cite]10.1021/ja00830a009[/cite] Nick Greeves, purveyor of the excellent ChemTube3D site, contacted me about the transition state (I have commented previously on this aspect of aromatic