https://doi.org/10.1351/goldbook.A00247
A @[email protected] occurring at position 1/ of an @[email protected] system, the double bond being between positions 2/ and 3/. The incoming group may be attached to the same atom 1/ as the @[email protected], or the incoming group becomes attached at the relative position 3/, with movement of the double bond from 2/3 to 1/2. For example:
A00247.png
(written as a @[email protected]).