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In [[chemistry]], the '''Effective Molarity''' (denoted ''EM'')<ref name=Kirby>{{cite book|last=Kirby, AJ in|title=Advances in Physical Organic Chemistry|year=1980|publisher=Academic Press|location=London|isbn=9780120335176|pages=183–278}}</ref> is defined as the ratio between the first-order rate constant of an [[intramolecular reaction]] and the second-order rate constant of the corresponding intermolecular reaction (''Kinetic Effective Molarity'')<ref name=Kirby /><ref>{{cite book|last=Dougherty|first=Eric V. Anslyn ; Dennis A.|title=Modern physical organic chemistry|year=2006|publisher=University Science Books|location=Sausalito, Calif.|isbn=9781891389313|pages=496|edition=Dodr.}}</ref> or the ratio between the [[equilibrium constant]] of an [[intramolecular reaction]] and the [[equilibrium constant]] of the corresponding intermolecular reaction (''Thermodynamic Effective Molarity'').<ref name=Kirby /><ref>{{cite journal|last=Hunter|first=Christopher A.|coauthors=Anderson, Harry L.|title=What is Cooperativity?|journal=Angewandte Chemie International Edition|date=28 September 2009|volume=48|issue=41|pages=7488–7499|doi=10.1002/anie.200902490}}</ref> 

<math>EM_{kinetic} = {k_{intramolecular} \over k_{intermolecular}}</math>

<math>EM_{thermo} = {K_{intramolecular} \over K_{intermolecular}}</math>

EM has the dimension of concentration. High EM values always indicate greater ease of intramolecular processes over the corresponding intermolecular ones. Effective molarities can be used to get a deeper understanding of the effects of intramolecularity on reaction courses.<ref>{{cite journal|last=Krishnamurthy|first=Vijay M.|coauthors=Semetey, Vincent; Bracher, Paul J.; Shen, Nan; Whitesides, George M.|title=Dependence of Effective Molarity on Linker Length for an Intramolecular Protein−Ligand System|journal=Journal of the American Chemical Society|date=1 February 2007|volume=129|issue=5|pages=1312–1320|doi=10.1021/ja066780e}}</ref> In last decades, the frequency of use of effective molarity in scientific literature has shown a marked decrease, because this formalism is being progressively replaced by more important [[physical quantities]].

==See also==
*[[Cyclic compound]]
*[[Macrocycle]]
*[[Intramolecular reaction]]
*[[Polymerization]]

==References==

{{Reflist}}

[[Category:Physical organic chemistry]]