According to Herges[1],[2] the mechanism of single-step (concerted) reactions can be divided into three basic types; linear (e.g. substitution, elimination etc), pericyclic (e.g. Diels Alder) and a third much rarer, and hence very often overlooked type that was named coarctate. This is based on the topology of bond redistribution patterns, an explicit real example[3] illustrating:
References
- R. Herges, "Coarctate transition states: the discovery of a reaction principle", Journal of Chemical Information and Computer Sciences, vol. 34, pp. 91-102, 1994. http://dx.doi.org/10.1021/ci00017a011
- B.S. Young, R. Herges, and M.M. Haley, "Coarctate cyclization reactions: a primer", Chemical Communications, vol. 48, pp. 9441, 2012. http://dx.doi.org/10.1039/c2cc34026g
- C. Berger, C. Bresler, U. Dilger, D. Geuenich, R. Herges, H. Röttele, and G. Schröder, "A Spontaneous Fragmentation: From the Criegee Zwitterion to Coarctate Möbius Aromaticity", Angewandte Chemie International Edition, vol. 37, pp. 1850-1853, 1998. http://dx.doi.org/10.1002/(SICI)1521-3773(19980803)37:13/14<1850::AID-ANIE1850>3.0.CO;2-B