
	Where results make sense

Topic: Free radical halogenation

	Free Radical Halogenation Mechanism
		Free radical halogenation is a reaction that substitutes a chlorine or a bromine for a hydrogen on an alkane.
		A point of note about free radical processes is that the intermediates are so highly reactive and short lived that usually you obtain a mixture of products, even though there is preference for forming more highly substituted free radical intermediates.
		Free radical chlorination, though, would not be quite as selective, and there would be a greater amount of the chlorination of the primary carbon than in the bromination reaction.
	www.chemhelper.com /frhalog.html (649 words)

	Process for halogenating isomonoolefin copolymers - Patent 5681901 (Site not responding. Last check: 2007-11-05)
		Halogenated butyl rubber may be prepared using relatively facile ionic reactions by contacting the polymer, preferably dissolved in organic solvent, with a halogen source, e.g., molecular bromine or chlorine, and heating the mixture to a temperature ranging from about 20.degree.
		Increased halogenation efficiency is achieved by conducting the reaction under free radical halogenation conditions and in the presence of an oxidizing agent, e.g., hydrogen peroxide, which oxidizes hydrogen halide generated in-situ in the reaction back to free halogen.
		Halogen consumption is indicated, where molecular bromine is used as the halogenating agent, by a change in color of the reaction mixture from reddish brown to a light tan or amber color.
	www.freepatentsonline.com /5681901.html (3105 words)

	Free radical halogenation at AllExperts
		In chemistry free radical halogenation is a type of halogenation.
		A bromine radical is not very reactive and the transition state for proton abstraction has much radical character and is reached late.
		When the alkyl radical is fully formed in the transition state it can benefit fully from any resonance stabilization present thereby maximizing selectivity.
	en.allexperts.com /e/f/fr/free_radical_halogenation.htm (428 words)

	Reactive distillation process for free radical halogenation - Patent 5449801
		Free radical halogenation is a well known reaction that is often carried out under a variety of conditions.
		The generated halogen radicals undergo reaction with compounds of Formula II according to Equation 1 in the liquid and vapor phase.
		The halogen X.sub.2 is fed into the bottom of reaction zone H from source J. When the vapor reaches the X.sub.2 feed zone, it intimately mixes with X.sub.2.
	www.freepatentsonline.com /5449801.html?highlight=4101397 (4422 words)

	e-Assignment #2
		Free radical halogenation was explored in Chem 501 in terms of its mechanism, enthalpy, and reactivity.
		Heat, light or an initiatior induce homolytic cleavage of the halogen molecule to produce to radicals.
		Stops propagation by removing the radical necessary for it to continue; cut down on the efficiency of the overall reaction.
	www.sas.upenn.edu /~higginsa/eAssignment2.html (760 words)

	Free radical halogenation - Wikipedia, the free encyclopedia
		Free radical halogenation in organic chemistry is a type of halogenation.
		Hence the reaction of alkanes with fluorine is difficult to control, that with chlorine is moderate to fast, that with bromine is slow and requires high levels of UV irradiation while the reaction with iodine is practically non-existent and thermodynamically unfavorable.
		Halogenation often does not stop at monosubstititution, depending on reaction conditions the chlorination of methane yields dichloromethane, chloroform and tetrachloromethane.
	en.wikipedia.org /wiki/Free_radical_halogenation (1019 words)

	Radical substitution
		Keep in mind that radical chlorination of alkanes is less selective than the corresponding bromination since chlorine radicals are much more reactive (and therefore much less selective).
		The carbon radical is now in need of finding an extra electron, and will abstract a bromine atom when it encounters a bromine molecule.
		Since no new radical is formed, the chain cannot be propagated and the reaction eventually comes to a halt.
	www.as.ysu.edu /~pnorris/public_html/Mechanisms/radicalsub.htm (374 words)

	Alkane Reactivity
		Halogenation is the replacement of one or more hydrogen atoms in an organic compound by a halogen (fluorine, chlorine, bromine or iodine).
		Unlike the complex transformations of combustion, the halogenation of an alkane appears to be a simple substitution reaction in which a C-H bond is broken and a new C-X bond is formed.
		The most plausible mechanism for halogenation is a chain reaction involving neutral intermediates such as free radicals or atoms.
	www.cem.msu.edu /~reusch/VirtualText/funcrx1.htm (1653 words)

	[No title]
		A process that forms a free radical from a species with paired electrons is called the initiation step of the free radical reaction.
		Reactions in which a molecule and a free radical react to form a new molecule and a new radical are called propagation steps.
		Draw structures for the possible alkyl free radical intermediates that could be formed from each isomer by hydrogen abstraction by a bromine radical.
	people.uis.edu /gtram1/organic/alkylHalides/freeradicalhalogenation.htm (659 words)

	Halogenation – Web Listings
		Halogenation is a chemical reaction that replaces a hydrogen atom with a halogen atom.
		The reaction of alkenes with halogens (fluorine, chlorine, bromine and iodine.
		Mechanism for Halogenation of Benzene, the aromatic substitution of a halogen to a benzene ring.
	www.business.com /directory/chemicals/catalysts/halogenation/weblistings.asp (334 words)

	Alkyl halide (Site not responding. Last check: 2007-11-05)
		As is noted, the naming convention involves the halogen as a prefix to the alkane.
		The double bond of the alkene is replaced by two new bonds, one to the halogen and one to the hydrogen atom of the hydrohalic acid.
		There is a polarity about halogenoalkanes - the carbon to which the halogen is attached is slightly electropositive where the halogen is slightly electronegative.
	alkyl-halide.iqnaut.net (762 words)

	Ethane - Wikipedia, the free encyclopedia
		During the period 1847–1849, in an effort to vindicate the radical theory of organic chemistry, Hermann Kolbe and Edward Frankland produced ethane by the reductions of propionitrile (ethyl cyanide) and ethyl iodide with potassium metal, and, as did Faraday, by the electrolysis of aqueous acetates.
		At the anode, acetate is oxidized to produce carbon dioxide and methyl radicals, and the highly reactive methyl radicals combine to produce ethane:
		An important series of reaction in ethane combustion is the combination of an ethyl radical with oxygen, and the subsequent breakup of the resulting peroxide into ethoxy and hydroxyl radicals.
	en.wikipedia.org /wiki/Ethane (1487 words)

	Organic Chemistry: Chapter 6 (Site not responding. Last check: 2007-11-05)
		Although free-radical halogenation is not a good synthetic method in most cases, free-radical bromination of alkenes can be carried out in a highly selective manner.
		Allylic intermediates (cations, radicals, and anions) are stabilized by resonance with the double bond, allowing the charge or radical to be delocalized.
		This radical reacts with Br regenerating a bromine radical that continues the chain reaction.
	myphlip2.pearsoncmg.com /altproducts/demo/ab2page.cfm?vbcid=8993&vid=9718 (935 words)

	free radical chain chlorination (Site not responding. Last check: 2007-11-05)
		It is known that hydrogens on secondary carbons are more reactive to free radical halogenation than hydrogens located on the primary carbons of an alkane.
		The electron-attracting effect of the chlorine on C-1 increases the energy of the transition state during the abstraction of hydrogen by another chlorine radical on C-2.
		They are not only located on a secondary carbon where less energy is required to remove a hydrogen and where a more stable radical forms compared to primary carbons, but they are further away from the chlorosubstituent on C-1 and its influence.
	www.sas.upenn.edu /~bakerlee/freeradicalchainchlorination.html (419 words)

	Organic Chemistry: Chapter 6
		Although free-radical halogenation is not a good synthetic method in most cases, free-radical bromination of alkenes can be carried out in a highly selective manner.
		Allylic intermediates (cations, radicals, and anions) are stabilized by resonance with the double bond, allowing the charge or radical to be delocalized.
		This radical reacts with Br regenerating a bromine radical that continues the chain reaction.
	myphlip.pearsoncmg.com /altproducts/phdemo/ab2page.cfm?vbcid=8993&vid=9718 (936 words)

	addition (Site not responding. Last check: 2007-11-05)
		A conceptually different type of mechanism to those encountered so far is the free radical halogenation of unactivated alkanes to broduce haloalkane products.
		The radical bromination is initiated by cleavage of a relatively weak Br-Br bond using either heat or UV light as the energy source.
		When the Br radical encounters the alkane substrate, it will "strip off" a hydrogen atom along with one of the C-H bond electrons..
	iws.ohiolink.edu /chemistry/organic/bromination.html (366 words)

	card14 Benzylic free-radical substitution (Site not responding. Last check: 2007-11-05)
		Removal of H by a radical from the benzylic C is easier than in an 'ordinary' alkane (like methane).
		This is because the radical can be delocalized over the adjacent aromatic ring (as represented by the appropriate resonance structures).
		The more reactive of the four resonance structure for benzylic radical is the benzylic C radical, of course, since it can be halogenated to produce an aryl (more stable) produce, while addition at any of the ring C's will produce a non-aryl product.
	www.mc.edu /campus/users/valente/classes/ch304/card14.htm (135 words)

	Free Radical Halogentation (Site not responding. Last check: 2007-11-05)
		The reaction begins with the formation of chlorine radicals.
		The free radicals then react with the methane in a two step propagation:
		This process will ordinarily be repeated a large number of times.
	web.tampabay.rr.com /rpendarv/radical-chlorination/halogenation-mechanism.htm (80 words)

	Free Radical Halogenation
		The reaction begins with an initiation step: the separation of the halide into its radicals by the addition of ultra-violet light.
		Termination steps for free radical reactions are when the radicals collide.
		In this reaction, the halide radical will attack primarily in the place that will yield the most substituted alkyl radical.
	www.cartage.org.lb /en/themes/Sciences/Chemistry/Organicchemistry/CommonReaction/FreeRadical/FreeRadical.htm (191 words)

	Propagation step in free-radical halogenation.
		Isobutane with a radical in the center carbon would be the result of a homolytic cleavage.
		Heterolytic cleavage means, both of the electrons (in a bond) end up residing in one of the cleaved parts, and not equally shared.
		Due to a radical, alkane cleaves homolytically to form a alkyl radical.
	www.chemicool.com /forum/about729.html (208 words)

	Free Radical Halogenation of Alkanes
		Alkanes react with molecular halogens (typically Cl2 and Br2) to form alkyl halides.
		Alkyl halides are hydrocarbons that contain at least one halogen atom.
		These reactions take place at high temperatures or in the presence of UV light (symbolized by h?).
	www.albany.edu /faculty/musah/achm216a/presentations/chapter4/sld021.htm (41 words)

	Intute: Science, Engineering and Technology - Search results
		The topics reviewed are: the alkyl halides, industrial sources of alkyl halides, alkyl halide preparation from alcohols, halogenation of hydrocarbons, the addition of HX to alkenes, the addition of hydrogens to alkynes and alkenes, Finkelstein reactions, nucleophilic substitution, carbocation (stability, rearrangements and stereochemical consequences), polar aprotic solvents and solvent polarity.
		The topics covered are: reactions of alkanes, initiation, arrow notations, free radical halogenation of methane, the propagation reaction, the termination reaction, stability of radicals, and the determination of the number and ratio of chlorination products.
		Notes are provided on aromaticity, resonance forms, electrophilic aromatic substitution, substituent effects, Friedel-Crafts alkylation and acylation, Friedel-Crafts halogenation, sulphonation, nitration, electrophilic substitution of naphthalene, and electrophilic substitution of aniline.
	www.intute.ac.uk /sciences/cgi-bin/search.pl?term1=halogenation&limit=0 (1070 words)

	JCE 2004 (81) 1661 [Nov] Free Radical Halogenation, Selectivity, and Thermodynamics: The Polanyi Principle and ...
		JCE 2004 (81) 1661 [Nov] Free Radical Halogenation, Selectivity, and Thermodynamics: The Polanyi Principle and Hammond's Postulate
		Free Radical Halogenation, Selectivity, and Thermodynamics: The Polanyi Principle and Hammond's Postulate
		Free radical halogenation reactions are examined in the contexts of the Polanyi principle and Hammond's postulate and used as a vehicle for examination of the concept of selectivity in chemical reactions.
	jchemed.chem.wisc.edu /journal/issues/2004/Nov/abs1661.html (203 words)

	Free Radical Halogenation (Site not responding. Last check: 2007-11-05)
		If the methyl radical reacts with another radical, it will give an non radical product which will end the reaction chain.
		Even though the first reaction produces the chlorinated product, it ends the chain reaction and will not continue to make more molecules of the product.
		This is not consistent with the evidence that a small amount of light can result in many chlorinations.
	www.cfcc.cc.fl.us /~pendarvr/mechanisms/radical-chlorination/u-mechanism-4wrong-t.htm (136 words)

	Halogenation - Wikipedia, the free encyclopedia
		An example of halogenation can be found in the organic synthesis of the anesthetic halothane from trichloroethylene which involves a high temperature bromination in the second step
		It has been shown that the reaction of bromine water, for instance, in ethene caused the formation of 2-bromoethanol.
		This page was last modified 12:52, 11 December 2006.
	en.wikipedia.org /wiki/Halogenation (219 words)

	Free Radical Halogenation (Site not responding. Last check: 2007-11-05)
		Homolysis of Cl into free radicals is the first step.
		When the chlorine radical reacts with the methane, it abstracts a hydrogen atom with its associated electron leaving a methyl radical.
		The methyl radical produced has an unpaired electron.
	web.tampabay.rr.com /rpendarv/radical-chlorination/u-mechanism-4.htm (64 words)

	Chem 246H: Organic Free Radical Chemistry
		M. Perkins "Radical Chemistry" Ellis, Horwood, New York, 1994.
		B. Giese "Radicals in Organic Synthesis: Formation of Carbon-Carbon Bonds" Pergamon, Oxford, 1986.
		D. Curran, N. Porter, B. Giese, "Stereochemistry of Radical Reactions," VCH, Weinheim, 1996.
	www.chemistry.ucsc.edu /teaching/braslau/chem246H.html (111 words)

	Chemistry 201 - CAlkyl Halides (Site not responding. Last check: 2007-11-05)
		Halogenation of Alkanes - Free Radical Chlorination of CH4
		Halogenation of Alkanes with Multiple Classes of Hydrogens
		Relative Rates of Chlorination: A Function of Radical Stabilities
	www6.miami.edu /chem/chm201c/notes/ch10/index.htm (26 words)

	Experiment 3: Free Radical Chlorination
		Chapter 10 in Jones covers radicals, radical reactions, and radical chain mechanisms
		The overall reaction for the free radical chlorination is the following.
		For the report you will be asked several questions about the product mixture.
	www.ipfw.edu /chem/266/266n0205.htm (572 words)

	Chemistry - Organic reaction
		Here are some common reactions that you may run into in a college organic chemistry course: addition of HX to an alkene, halogen addition reaction, halohydrin formation reaction, oxymercuration reaction, hydroboration-oxidation reaction, hydrooxylation reaction, ozonolysis reaction, nucleophilic substitution, halogenation of an alkyl, hydration and dehydration.
		Here is a series of reactions that a chemist can perform to change molecules in a defined way: Beckmann rearrangement, Friedel-Crafts alkylation and acylation, Gilman reagent, Grignard reagent, Diels-Alder reaction, Pinner reaction, Sharpless epoxidation, Sharpless bishydroxylation, Swern oxidation
		(RS) Free radical bromination: alkene + N-bromosuccinaimide (NDS) -> brominated at allylic position, without addinng to double bond.
	www.chemistrydaily.com /chemistry/Organic_reaction (474 words)

Try your search on: Qwika (all wikis)