A substitution reaction occurring at position 1/ of an allylic system, the double bond being between positions 2/ and 3/. The incoming group may be attached to the same atom 1/ as the leaving group, 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:
(written as a transformation).
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1082 (https://doi.org/10.1351/pac199466051077)