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Topic: Carbanion

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	Carbanion - Wikipedia, the free encyclopedia
		A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons.
		The stability and reactivity of a carbanion is determined by several factors.
		A carbanion is a reactive intermediate and is encountered in organic chemistry for instance in the E1cB elimination reaction and in organometallic chemistry in for instance a Grignard reaction or in alkyl lithium chemistry.
	en.wikipedia.org /wiki/Carbanion (209 words)

	Anionic addition polymerization - Wikipedia, the free encyclopedia
		An anionic addition polymerization of vinyl monomers is an addition polymerization initiated by a strong base and anion, such as an alkali amide, or an organometallic compound, such as n-butyllithium.
		A nucleophilic carbanion is formed containing an unshared pair of electrons.
		Confronted with a carbon molecule with a terminal double bond, such as ethene and a wide variety of monomer vinyl compounds as styrene or acrylonitrile, a conjugate addition occurs between the terminal carbon atom of the carbanion and the first carbon atom of the C = C bond.
	en.wikipedia.org /wiki/Anionic_addition_polymerization (271 words)

	Carbanions - Chemistry Professor - Organic, Inorganic, High School, College, Chemistry Tutor - ChemistryProfessor.com
		Carbanions introduces the characteristic reactions occurring at the alpha hydrogen of carbonyls.
		This unit on carbanions begins with a treatment of the alpha hydrogen and its significantly acidic character, a factor which permits reaction with a particularly strong base, such as lithium diisopropylamide.
		The rearrangement of the carbanion under appropriate conditions to form the familiar enolate ion and subsequently keto-enol tautomerism is addressed.
	chemistryprofessor.com /carbanions.htm (558 words)

	carbanion -- Encyclopædia Britannica (Site not responding. Last check: 2007-10-14)
		Carbanions are formally derived from neutral organic molecules by removal of positively charged atoms or groups of atoms, and they are important chiefly as chemical intermediates—that is, as substances used in the preparation of other substances.
		In the former, the negative charge is confined largely to one carbon atom, whereas, in the latter, it is distributed over several atoms.
		Perhaps the most common reaction of carbanions is their action as bases—as shown in the first equation in this article.
	www.britannica.com /eb/article-9020235 (301 words)

	Reactions involving carbanions (Site not responding. Last check: 2007-10-14)
		Carboxylic acids are acidic due to the stability of the resonance hybrid carbanion.
		The carbonyl carbon is subject to nucleophillic attack due to the ability of the intermediate to accommodate a negative charge.
		In the presence of an alkoxide ion the a hydrogen of a carboxylic acid ester is abstracted to form a carbanion.
	webpages.charter.net /markbishop/Organic/Carbanions.htm (425 words)

	card38 Reduction of esters with Grignard reagent (Site not responding. Last check: 2007-10-14)
		Use of carbanion (from Grignard reagents) to reduce esters proceeds to the alcohol.
		Since this occurs with C-C bond formaton, the alcohol formed is tertiary, with two of the three "R" groups on the tertiary C having come from the Grignard reagent.
		The ketone is susceptible of attack by a second equivalent of Grignard reagent (2 equivalents being necessary for the complete reaction), which leads to the tertiary alkoxide.
	www.mc.edu /campus/users/valente/classes/ch304/card38.htm (125 words)

	Thiamine
		TPP is a coenzyme for two types of enzymes, alpha-ketoacid dehydrogenases and transketolases, both of which cleave a C-C bond adjacent to a carbonyl group releasing either carbon dioxide or an aldehyde.
		In the reaction, a carbanion at C-2 of TPP is first produced.
		This glycoaldehyde is said to be activated because it is also a carbanion and readily undergoes nucleophilic addition to the carbonyl group of an aldose (erythrose 4-phosphate here).
	www.angelfire.com /ak2/chemists/stan6.html (1487 words)

	Effect of Substituents on Carbanion Stability
		All measures of acidity show that there is an unusual level of carbanion stabilization for all second row elements (Cl, S, P, Si, as well as higher elements) when these are bonded to a carbanion center.
		In the carbanion the C orbital increases in size, resulting in a stronger sigma bond.
		This has several effects on carbanion structure: there are substantial rotational barriers around the C-X bond and the carbanion center is usually more pyramidalized.
	www.chem.wisc.edu /areas/reich/chem842/_chem842-01-intro{03}.htm (504 words)

	CA 38 Skill Development Exercises for Part B (Site not responding. Last check: 2007-10-14)
		Carbocations and carbanions follow the opposite trend in terms of the energy of primary, secondary and tertiary.
		However, an allyl (allyllic) carbanion is much lower energy than a primary carbanion, and a benzyl (benzyllic) carbanion is even lower in energy.
		This is because of the very strong resonance effects of a benzyl carbanion.
	home.earthlink.net /~cuachemistry/organic/SDEAns/AnsSDE38B.htm (225 words)

	[No title]
		In cycloimmonium ylids [2,3] nitrogen belonging to the azo-heterocycle is covalently bonded to a mono- or di-substituted carbanion (Fig.1).
		1 Carbanion mono-substituted (a) and di-substituted (b) cycloimmonium ylids.The ylid aromatic nitrogen is near sp2 hybridizated in all circumstances, while for the ylid carbanion sp2 and sp3 are two limits of hybridization.
		An increase of the conjugation in the case of carbanion disubstituted planar cycloimmonium ylids determined by electron withdrawing groups attached to the carbanion shifts hypsochromically the maximum of the UV absorption bands.
	www.itim-cj.ro /PIM/2003/FullText/oral/Dorohoi.doc (1782 words)

	The Fluoride Ion and The Carbanions
		Thus, organic chemistry with its special emphasis on the C–C bond has the fluoride ion, F–, harder than the carbanion at delta+ carbon centres whereas the chloride, bromide and iodide are softer.
		It is possible to have carbanion and oxyanion centres in the same function, as seen with the enolate ion:
		The reactivity of a carbanion can be modified by the nature of the positive counter ion.
	www.meta-synthesis.com /webbook/10_fluoride/fluoride.html (1378 words)

	Reaction intermediates - Carbanions (Site not responding. Last check: 2007-10-14)
		Many substituted carbanions have been studied and serve to establish quantitative kinetic parameters for several types of well known nucleophilic substitution reactions.
		We have also been able to demonstrate that the lifetime of these carbanions can be extended by encapsulation in zeolites, where they show Grignard-like reactivity.
		Most recently we have been able to increase the lifetime of the ketoprofen carbanion to several minutes, by preparing it in dry THF containing NaH.
	photo.chem.uottawa.ca /project6.htm (229 words)

	OUP: Carbanion Chemistry: Buncel
		Carbanions and other group 14 anions are fundamental reaction intermediates in organic chemistry and are central in mechanistic studies and in synthesis.
		This book describes their properties and structures, the conditions under which they form, and the factors that affect their thermodynamic and kinetic stability.
		Important chapters on the spectroscopy of these group 14 anions and on carbanion reactions catalyzed by heterogenous solid base catalysis are included.
	www.oup.co.uk /isbn/0-8412-3556-2?view=00&promo=websocrsc (227 words)

	Ch 9 : Acidity of Terminal Alkynes
		This carbanion can be used as a C centered nucleophile.
		For each type of carbanion shown, the nature of the hybrid orbital containingthe electron pair is important.
		However the terminal alkyne C-H bond is not strongly acidic and a strongbase, such as the amide ion, NH, is required toform the carbanion.
	www.chem.ucalgary.ca /courses/351/Carey5th/Ch09/ch9-2.html (184 words)

	LECTURE 5
		O, deuterium is incorporated into the methyl group; this is the result of a less rapid attack of the carbanion on a carbonyl carbon atom which is markedly less positive than that of an aldehyde.
		In this case the carbonyl compounds act as the carbanion acceptor because the carbanion formed by the nitro compound tends to be the more stable as it has a more effective delocalisation of its charge.
		The phosphorous ylides have hybrid structures, and it is the negative charge on carbon (the carbanion in the ylide) that is responsible for their nucleophilic attack on carbonyl carbon.
	www.uiowa.edu /intlinet/unijos/departments/pharmacology/additional.htm (1340 words)

	Introduction
		The collapse ratio may be influenced by the structure of the carbanion as well as the proton-abstracting base.
		The protonated base might be hydrogen bonded to the carbanion throughout the rearrangement, which then proceeds intramolecularly, or it might partly or totally diffuse into the solvent leaving the carbanion more or less free.
		The suggested intermediates are tightly hydrogen bonded ion pairs between the protonated amine and the carbanion.
	www.kvac.uu.se /~agback/science/Paper1.9.html (3425 words)

	card23 Carbanion reduction of aldehydes and ketones (Site not responding. Last check: 2007-10-14)
		Carbanion (R:-) is an effective nucleophilic reducing agent for aldehydes and ketones generally.
		) is nucleophilic attack at the carbonyl carbon by the "carbanion" to form the alkoxide.
		Most typically, one uses the Grignard reagent for the carbanion source.
	www.mc.edu /campus/users/valente/classes/ch304/card23.htm (100 words)

	[No title] (Site not responding. Last check: 2007-10-14)
		The alkyl portion of the Grignard reagent behaves as a carbanion.
		In the second step of the Grignard reaction, the carbanion reacts as a nucleophile, attacking the electropositive carbon of a carbonyl.
		In this application, the carbanion reacts with the electropositive center of carbon dioxide to generate a carboxylate salt.
	www.coloradocollege.edu /dept/ch/ch250/Laboratory/grignard.2.doc (1338 words)

	[No title]
		The product carbanion is shown as a zwitterion in the lefthand structure.
		However, this ylide, regardless of which of the two resonance forms shown better represent its physical structure, reacts as if it were the charged species: as a nucleophilic carbanion.
		The ylide is then treated with a carbonyl compound, in this case cinnamaldehye, Ph-CH=CH-CH=O. The carbanion bonds to the carbonyl carbon, and the oxygen of the C=O becomes bonded to the phosphorous, in a 4 membered ring.
	web.utk.edu /~bartmess/wittig.html (1044 words)

	4-(4-Chlorophenyl)pyrimidinium ylides. 1. Structure, stability, reactivity. (Site not responding. Last check: 2007-10-14)
		This absorption band is very sensitive to ylide carbanion substituents and, secondly, to the nature of the solvent.
		The wavelengths of the ICT band maximum depend on the carbanion substituents. When X is a nitro group, the electron-withdrawing effect is stronger and there is an advanced delocalization of the anionic charge.
		The higher the delocalization of the negative charge along the carbanion is, the higher the wavenumber of the ICT band will be.
	www.arkat-usa.org /ark/journal/2005/I01_General/1206/04-1206B.asp (3594 words)

	Ion pairs. (from carbanion) -- Encyclopædia Britannica (Site not responding. Last check: 2007-10-14)
		In a solution containing carbanions there must exist a corresponding cation (positive ion) for each carbanion.
		If the two ions of opposite charge are in close contact with each other, a covalent (nonionic) bond may form.
		Because for a given carbanion the reaction of ionization…
	www.britannica.com /eb/article-1108 (742 words)

	LECTURE 5
		The corresponding reaction of acetone to diacetone alcohol proceeds much more slowly and, when carried out in D2O, deuterium is incorporated into the methyl group; this is the result of a less rapid attack of the carbanion on a carbonyl carbon atom which is markedly less positive than that of an aldehyde.
		The carboxylate anion abstracts a proton from the a-carbon of the anhydride to form carbanion I. This carbanion undergoes nucleophilic addition to carbonyl carbon of the aldehyde.
		This is because the a-hydrogen of b-keto ester are located a to two carbonyl groups and hence ionization yields a particularly stable carbanion in which two carbonyl groups help to accommodate the charge.
	www.uiowa.edu /intlinet/unijos/departments/pharmacology/Afolabi/add.react.htm (1400 words)

	Photochemistry and Photobiology: Laser flash photolysis of tolmetin: A photoadiabatic decarboxylation with a triplet ...
		Photochemistry and Photobiology: Laser flash photolysis of tolmetin: A photoadiabatic decarboxylation with a triplet carbanion as the key intermediate in the photodecomposition
		Laser flash photolysis of tolmetin: A photoadiabatic decarboxylation with a triplet carbanion as the key intermediate in the photodecomposition
		The photoreactivity of TM is characterized by an adiabatic pathway involving a triplet carbanion as the key intermediate in the photodecarboxylation.
	www.findarticles.com /p/articles/mi_qa3931/is_199902/ai_n8834755 (1339 words)

	Alkylation of Terminal Alkynes (Site not responding. Last check: 2007-10-14)
		The acetylide carbanion is a good C nucleophile and can undergo nucleophilic substitution reactions (usually SN2) with 1
		The amide ion acts as a base removing the acidic terminal H to generate the acetylide ion, a carbon nucleophile.
		The carbanion reacts with the electrophilic carbon in the alkyl halide with loss of the leaving group, forming a new C-C bond.
	library.tedankara.k12.tr /carey/ch9-3.html (181 words)

	On the reaction mechanism of L-lactate oxidase: Quantitative structure-activity analysis of the reaction with ...
		It is beyond the scope of this paper to describe in detail the experimental evidence in support of the "carbanion" mechanism,
		are consistent with the operation of a carbanion
		To reiterate, the present results are not compatible with a carbanion mechanism in its classical formulation, i.e., one in
	www.pnas.org /cgi/content/full/94/18/9590 (3151 words)

	Ylidic polyfunctionalized compounds with a diazinium skeleton (Site not responding. Last check: 2007-10-14)
		For the first time in the cycloimmonium ylide series we have obtained unsaturated styryl carbanion monosubstituted ylides.
		Since then no other research has been done in the field of diazinium ylides with unsaturated carbanion although this is a convenient way to acces polyfunctionalized compounds with a ylidic skeleton.
		Thus, the reactions of phtalazine and 4-methylpyrimidine with cinnamyl bromide yield to the salts 1 and 2, respectively.
	www.arkat-usa.org /ark/journal/2001/I10_Undheim/165/165A.asp (2026 words)

	Birch Reduction
		When viewed in valence bond terms, electron-electron repulsions in the radical anion will preferentially have the nonbonding electrons separated as much as possible, in a 1,4-relationship.
		The numbers, which stand for the number of bonds, can be averaged and compared with the 1,3- and the 1,4-diene.
		The difference between the dienyl carbanion and 1,3-diene in absolute numbers is 2, and between the dienyl carbanion and 1,4-diene is 4/3.
	www.organic-chemistry.org /namedreactions/birch-reduction.shtm (221 words)

	carbanion - OneLook Dictionary Search
		carbanion : Stedman's Online Medical Dictionary, 27th Edition [home, info]
		carbanion : Encarta® World English Dictionary, North American Edition [home, info]
		carbanion : The American Heritage® Dictionary of the English Language [home, info]
	www.onelook.com /?ls=b&fc=all_med&q=carbanion (95 words)

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