Editing Nucleophile (section)

==== Swain–Scott equation ====
The first such attempt is found in the Swain–Scott equation<ref>{{Cite journal |last=Swain |first=C. Gardner |last2=Scott |first2=Carleton B. |date=January 1953 |title=Quantitative Correlation of Relative Rates. Comparison of Hydroxide Ion with Other Nucleophilic Reagents toward Alkyl Halides, Esters, Epoxides and Acyl Halides 1 |url=https://pubs.acs.org/doi/abs/10.1021/ja01097a041 |journal=Journal of the American Chemical Society |language=en |volume=75 |issue=1 |pages=141–147 |doi=10.1021/ja01097a041 |issn=0002-7863|url-access=subscription }}</ref><ref>{{cite book |doi=10.1351/goldbook.S06201 |doi-access=free |chapter=Swain–Scott equation |title=The IUPAC Compendium of Chemical Terminology |year=2014 }}</ref> derived in 1953:
:<math>\log_{10}\left(\frac{k}{k_0}\right) = sn</math>

This [[free-energy relationship]] relates the [[pseudo first order reaction|pseudo first order]] [[reaction rate constant]] (in water at 25&nbsp;°C), ''k'', of a reaction, normalized to the reaction rate, ''k''<sub>0</sub>, of a standard reaction with water as the nucleophile, to a nucleophilic constant ''n'' for a given nucleophile and a substrate constant ''s'' that depends on the sensitivity of a substrate to nucleophilic attack (defined as 1 for [[methyl bromide]]).

This treatment results in the following values for typical nucleophilic anions: [[acetate]] 2.7, [[chloride]] 3.0, [[azide]] 4.0, [[hydroxide]] 4.2, [[aniline]] 4.5, [[iodide]] 5.0, and [[thiosulfate]] 6.4. Typical substrate constants are 0.66 for [[tosylate|ethyl tosylate]], 0.77 for [[lactone|β-propiolactone]], 1.00 for [[epoxide|2,3-epoxypropanol]], 0.87 for [[benzyl chloride]], and 1.43 for [[benzoyl chloride]].

The equation predicts that, in a [[nucleophilic displacement]] on [[benzyl chloride]], the [[azide]] anion reacts 3000 times faster than water.