Effective molarity
{{Short description|Ratio used in chemistry}}
In chemistry, the effective molarity (denoted EM){{cite book|last=Kirby, AJ in|title=Advances in Physical Organic Chemistry|year=1980|publisher=Academic Press|location=London|isbn=9780120335176|pages=183–278}} 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){{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.}} or the ratio between the equilibrium constant of an intramolecular reaction and the equilibrium constant of the corresponding intermolecular reaction (thermodynamic effective molarity).{{cite journal|last=Hunter|first=Christopher A.|author2=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}}
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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.{{cite journal|last=Krishnamurthy|first=Vijay M.|author2=Semetey, Vincent |author3=Bracher, Paul J. |author4=Shen, Nan |author5= 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 |pmid=17263415 |pmc=2535942}}
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