The primary @[email protected] in a mechanistic change; usually either of the two atoms of a transformed multiple bond or the single atom at which substitution occurs.
Source: PAC, 1989, 61, 23. (System for symbolic representation of reaction mechanisms (Recommendations 1988)) on page 55 [Terms] [Paper]
Cite as: IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S. J. Chalk. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.