Zucker-Hammett hypothesis

{
  "id": "MLC-T-CHM-012819",
  "term": "Zucker-Hammett hypothesis",
  "field": "Chemistry",
  "definition": "A mechanistic criterion for acid-catalysed reactions that links the acid dependence of the rate to the role of water in the rate-limiting step. A rate constant whose logarithm is linear in the Hammett acidity function H0 was taken to mean that water is absent from the transition state, as in a unimolecular step of the protonated substrate, whereas linearity in the logarithm of hydrogen-ion concentration was taken to mean that water takes part. Hammett himself later showed the criterion to be unreliable.",
  "subject": "Organic and Biomolecular Chemistry",
  "see_also": [
    "acidity function",
    "order of reaction",
    "rate-controlling step",
    "transition state"
  ],
  "references": [
    "PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1176 (https://doi.org/10.1351/pac199466051077)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/zucker-hammett-hypothesis/"
}