en>AMALGARAI at 16:34, 10 January 2015

2015-01-10T16:34:47Z

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	~~In [[chemistry]] the '''reactivity–selectivity principle''' or '''RSP~~'~~'' states that a more reactive [[chemical compound]] or [[reactive intermediate]] is less selective in chemical reactions. In this context selectivity represents the ratio of [[reaction rate]]~~s.		Marvella is what you can call her but it's not the most feminine name out there. Bookkeeping is what I do. To perform baseball is the pastime he will by no means stop doing. Her spouse and her reside in Puerto Rico but she will have to move one working day or an additional.<br><br>my page - [http://vei.cuaed.unam.mx/es/node/4882 std testing at home]

	~~This principle was generally accepted until~~ the ~~1970s when too many exceptions started to appear~~. ~~The principle~~ is now considered obsolete.<ref>''Minireview The Reactivity-Selectivity Principle: An Imperishable Myth in Organic Chemistry '' Herbert Mayr, Armin R. Ofial [[Angewandte Chemie International Edition]] Volume 45, Issue 12 , Pages 1844 - 1854 [http://dx.doi.org/10.1002/anie.200503273 Abstract]</ref>

	A classic example of perceived RSP found in older organic textbooks concerns the [[free radical halogenation]] of simple [[alkane]]s. Whereas the relatively unreactive [[bromine]] reacts with 2-methylbutane predominantly to 2-bromo-2-methylbutane, the reaction with much more reactive [[chlorine]] results in a mixture of all four [[regioisomer]]s.

	~~Another example of RSP can be found in the selectivity of the reaction of certain [[carbocation]]s with [[azide]]s and [[water]]~~. The very stable triphenylmethyl carbocation derived from [[solvolysis]] of the corresponding [[triphenylmethyl chloride]] reacts 100 times faster with the azide anion than with water. When the carbocation is the ~~very reactive tertiary [[adamantane]] carbocation (as judged from diminished [[reaction rate\|rate]] of solvolysis) this difference is only a factor of 10~~.

	~~Constant or inverse relationships are just as frequent. For example a group of 3-~~ and ~~4-substituted [[pyridine]]s~~ in ~~their reactivity quantified by their [[pKa]] show the same selectivity in their reactions with a group of alkylating reagents.~~

	The reason for the early success of RSP was that the experiments involved very reactive intermediates with reactivities close to [[kinetic diffusion control]] and as a result the more reactive intermediate appeared to ~~react slower with the faster substrate.~~

	~~General relationships between reactivity and selectivity in chemical reactions can successfully explained by [[Hammond's postulate]].~~

	~~[[Image:ReactivitySelectivity.png\|right\|300px\|Tetrazole-Derived Thiyl radical]]When reactivity-selectivity relationships do exist they signify different reaction modes. In~~ one study <ref>''Search for High Reactivity and Low Selectivity of Radicals toward Double Bonds: The Case of a Tetrazole-Derived Thiyl Radical'' Jacques Lalevée, Xavier Allonas, and Jean Pierre Fouassier [[J. Org. Chem.]]; '''2006'''; 71(26) pp 9723 - 9727; (Article) {{DOI\|10.~~1021/jo061793w}}~~<~~/ref~~><~~ref~~>~~Sulfur [[tetrazole]] radical derived from [[photolysis]] of [[disulfide]] and carbon radical derived from photolysis of [[t~~-~~butylperoxide]] followed by proton abstraction from~~ [[triethylamine]]</ref> the reactivity of two different [[free radical]] species (A, sulfur, B carbon) towards addition to simple [[alkene]]s such as [[acrylonitrile]], [[vinyl acetate]] and [[acrylamide]] was examined.

	The sulfur radical was found to be more reactive (610<sup>8</sup> vs. 110<sup>7</sub> mole<sup>−1</sup>.s<sup>−1</sup>) and less selective (selectivity ratio 76 vs 1200) than the carbon radical. In this case the effect can be explained by extending the [[Bell–Evans–Polanyi principle]] with a factor <math>\delta \,</math> accounting for transfer of charge from the reactants to the [[transition state]] of the reaction which can be calculated [[in silico]]:

	~~<math>E_a = E_o + \alpha \Delta H_r + \beta \delta^2\,<~~/~~math>~~

	~~with <math>E_a\,<~~/~~math> the [[activation energy]] and <math>\Delta H_r\,</math> the reaction [[enthalpy]] change~~. With the [[electrophile\|electrophilic]] sulfur radical the charge transfer is largest with electron-rich alkenes such as acrylonitrile but the resulting reduction in activation energy (β is negative) is offset by a reduced enthalpy. ~~With the [[nucleophile\|nucleophilic]] carbon radical on the other hand both enthalpy and polar effects have the same direction thus extending the activation energy range~~.

	~~==External links==~~
	* Reactivity–selectivity principle [[Gold Book]] [http://~~www.iupac.org~~/~~goldbook/R05186.pdf Link]~~

	~~==References==~~
	~~{{Reflist}}~~

	~~{{DEFAULTSORT:Reactivity-selectivity principle}}~~
	~~[[Category:Obsolete scientific theories]]~~
	~~[[Category:Physical chemistry]~~]

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