Spectator mechanism

{
  "id": "MLC-T-CHM-011119",
  "term": "Spectator mechanism",
  "field": "Chemistry",
  "definition": "A pre-association mechanism in which a second species is already held in an encounter pair with the substrate while an intermediate forms from it, yet takes no part in forming that intermediate. The bystander is called a spectator because it simply waits to react with the short-lived intermediate once it appears. Pre-association matters when the intermediate lives too briefly to meet its partner by diffusion, which is why the partner must already be present.",
  "subject": "Organic and Biomolecular Chemistry",
  "see_also": [
    "molecularity",
    "microscopic diffusion control",
    "molecular entity",
    "pre-association"
  ],
  "references": [
    "PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1165 (https://doi.org/10.1351/pac199466051077)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/spectator-mechanism/"
}