Hammond's postulate
Predicts transition state structure from energy comparisons.
Last updated
Hammond's postulate is a hypothesis in physical organic chemistry that describes the geometric structure of the transition state in an organic chemical reaction.[1] By comparing a state's energy to that of its neighbors on the reaction coordinate, one can infer its geometric structure.[2] Since experimental characterization of transition states is generally not possible, this type of energy comparison proves particularly valuable.[2]
Quick Facts
- Field
- Physical organic chemistry
- Known for
- Hammond's postulate (Hammond–Leffler postulate)
Facts from the source article.
Key facts and history
George Hammond first proposed the postulate in 1955.[1] Chemists in the mid-20th century struggled to account for how minor alterations in starting materials could produce major shifts in reaction rates and product mixtures.[3] To acknowledge the contributions of both researchers, the concept is occasionally referred to as the Hammond–Leffler postulate.[4]
What the research sources say
The same source notes that an "early" transition state closely resembles the reactants, while a "late" transition state closely resembles the intermediate or product.[5][6] George Hammond's 1955 paper "A Correlation of Reaction Rates" in the Journal of the American Chemical Society is the original source of the postulate.[7][1] A 2001 activity published in the Journal of Chemical Education notes that Hammond's postulate allows the transition state structure to be discussed in relation to reactants, intermediates, or products.[5][6] A study in the Journal of the American Chemical Society from July 2015 describes a kinetic resolution process that begins with two energetically equivalent enantiomers and ultimately yields two energy-inequivalent intermediates.[8][9]
References
- Wikipedia, "Hammond's postulate" (CC BY-SA 4.0), which cites: Fox, "Organic Chemistry", Jones and Bartlett Publisher s, 2004, p. 355–357; Hammond, G. S., "A Correlation of Reaction Rates", J. Am. Chem. Soc., 1955, p. 334–338 (we also read that source) en.wikipedia.org
- Wikipedia, "Hammond's postulate" (CC BY-SA 4.0), which cites: Carey, "Advanced Organic Chemistry Part A:Structure and Mechanisms", Springer, 2007; Anslyn, "Modern Physical Organic Chemistry", University Science, 2006 (original not read by us) en.wikipedia.org
- Wikipedia, "Hammond's postulate" (CC BY-SA 4.0), which cites: Yarnell, "Hammond Postulate: 1955 paper used transition-state theory to explain structure-reactivity relationships", Chemical & Engineering News, 2003, p. 42; "Parameters for the Description of Transition States", Science, March 1953, p. 340–1 (we also read that source) en.wikipedia.org
- Wikipedia, "Hammond's postulate" (CC BY-SA 4.0), which cites: Yarnell, "Hammond Postulate: 1955 paper used transition-state theory to explain structure-reactivity relationships", Chemical & Engineering News, 2003, p. 42 (we also read that source) en.wikipedia.org
- John E. Meany, "Application of Hammond's Postulate. An Activity for Guided Discovery Learning in Organic Chemistry", Journal of Chemical Education (2001), doi:10.1021/ed078p204. OpenAlex metadata CC0; paper not read. doi.org
- Wikipedia, "Hammond's postulate" (CC BY-SA 4.0), which cites: "Application of Hammond's postulate", Journal of Chemical Education, 1 February 2001, p. 204 (we also read that source) en.wikipedia.org
- George S. Hammond, "A Correlation of Reaction Rates", Journal of the American Chemical Society (1955), doi:10.1021/ja01607a027. OpenAlex metadata CC0; paper not read. doi.org
- Kamalraj V. Rajendran, "Hammond Postulate Mirroring Enables Enantiomeric Enrichment of Phosphorus Compounds via Two Thermodynamically Interconnected Sequential Stereoselective Processes", Journal of the American Chemical Society (2015), doi:10.1021/jacs.5b04415. OpenAlex metadata CC0; paper not read. doi.org
- Wikipedia, "Hammond's postulate" (CC BY-SA 4.0), which cites: "Hammond Postulate Mirroring Enables Enantiomeric Enrichment of Phosphorus Compounds via Two Thermodynamically Interconnected Sequential Stereoselective Processes", Journal of the American Chemical Society, July 2015, p. (we also read that source) en.wikipedia.org
Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Hammond's postulate (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.
More in Organic Chemistry And Reaction Mechanisms
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Hammond's postulate (CC BY-SA 4.0).
- Word definitions: the , each quoted from its Wikipedia article.
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