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Topic: Enolate

	enolate
		A carbonyl compound with an alpha-hydrogen readily undergoes abstraction by a nucleophile to produce the enolate anion/carbanion.
		The reactions we discussed involve the carbanion form as the reactive form, considering the reactions involve this alpha-carbon attacking the carbonyl of another molecule.
		The carbonyl is reformed as the leaving group is identical to the initial attacking nucleophile, the alkoxide anion..
	www.milligan.edu /science/RDLura/OrgMech2a/enolate/enolate.htm (161 words)

	NationMaster - Encyclopedia: Enolate
		Under thermodynamic conditions (warmer temperatures, weak base, and protic solvent) equilibrium is established between the ketone and the two possible enolates, the enolate favoured is termed the "thermodynamic" enolate and is favoured because of its lower energy level than the other possible enolate.
		Lithium enolate derivatives of aldehydes or ketones may be formed at low temperature by slow addition of the carbonyl compound to an excess of LDA in THF (-78 ºC).
		The dominant enolborinate in all cases is that derived from the kinetically favored enolate anion.
	www.nationmaster.com /encyclopedia/Enolate (518 words)

	Forming Enolates Under Non-Basic Conditions
		The standard method of enolate generation is deprotonation of a carbon alpha to an electron-withdrawing group, where the electron-withdrawing group is anything from a carbonyl to a nitrile.
		Enolates, especially enolates generated with LDA, show a preference for formation of a six-membered transition state which exhibits stereochemical preference for specific stereoisomers depending upon the size of the groups associated with the enolate, and the groups associated with another carbonyl in an aldol-type coupling.
		Additionally, as the enolate oxide is formed five atoms away from the carbon with the bromine, it is entirely possible that a six-membered ring can form and give a convenient 1-pot method of forming a tetrahydropyan with two (or three) stereocenters (3) from a methyleneoxetane.
	www.ux1.eiu.edu /~mdruane/RI2005a.html (787 words)

	ENOLATE : Encyclopedia Entry
		The resonance from the enol is exactly analogous to that used to explain the acidity of phenols and consists of the delocalisation of the negative charge of the enolate ion to the alpha-carbon.
		The synthetic value is due to the nucleophilicity of α-carbon of enolate group.
		In ketones (a type of carbonyl) with acidic α-hydrogens on either side of the carbonyl carbon, selectivity of deprotonation may be achieved to generate the enolate directly from the ketone.
	www.bibleocean.com /OmniDefinition/Enolate (464 words)

	Untitled Document
		A double bond forms between the carbon atom that was bonded to the cyclopropane ring and the carbonyl carbon atom to form an enolate-type structure, with the magnesium atom coordinating with an oxygen atom that now has negative character.
		An ambient nucleophile, the enolate selectively undergoes reaction with imine 27 at the carbon atom instead of the oxygen atom, which is less nucleophilic than a carbanion.
		The reaction is a concerted cyclization in which the stereochemistry of all formed stereocenters is determined in one step, with the enolate attacking the electrophilic carbon atom of the carbon-nitrogen double bond.
	www.umich.edu /~chemh215/W06HTML/SSG2/ssg2/leadingquestion.htm (683 words)

	Enolate phenylacetone synthesis FAQ 1.0 (Site not responding. Last check: )
		Enolate chemistry is a fascinating field — much of it very cutting edge (though this ain’t.) Generally, what we have here is a strong base (i.e.
		Phenylacetone from acetone enolate is a reaction that’s been very well covered, since its such a classic, simple Sn1 reaction to study.
		In a procedure similar to that described above, the enolate derived from 0.73 ml (10.0 mmol) of acetone was allowed to react with 0.25 ml (2.4 mmol) of bromobenzene.
	www.designer-drugs.com /pte/12.162.180.114/dcd/chemistry/p2p.enolate.html (2007 words)

	Reference.com/Encyclopedia/Michael reaction
		As originally defined by Michael, the reaction is the addition of an enolate of a ketone or aldehyde to an α,β-unsaturated carbonyl compound at the β carbon.
		The HOMO of stabilized enolates has a large coefficient on the central carbon atom while the LUMO of many alpha, beta unsaturated carbonyl compounds has a large coefficient on the beta carbon.
		In the latter case, the stabilized carbonyl compound is deprotonated with a strong Base (hard enolization) or with a Lewis acid and a weak base (soft enolization).
	www.reference.com /browse/wiki/Michael_reaction (722 words)

	[No title] (Site not responding. Last check: )
		Enolate anions can undergo nucleophilic addition to carbonyl groups.
		In aldol condensations, an enolate anion undergoes nucleophilic addition to a ketone or aldehyde producing a
		Enolate anions of esters can undergo nucleophilic addition to the carbonyl group of another ester.
	people.uis.edu /gtram1/organic/a-substitution/aldol.htm (216 words)

	Professor Steve Davies
		Similarly, the diastereoselectivities observed for alkylation of the enolate of N -protected diketopiperazine 5 are superior to those of the related enolate of Schöllkopf's auxiliary.
		Enolate alkylation proceeds anti to both the N -lone pair and the bulky tert -butyl group (Figure 9B).
		The high and predictable levels of diastereoselectivity observed using our conjugate addition protocol 15 combined with stereoselective enolate elaboration has allowed an enormous range of b -amino acid derived structural motifs to be accessed readily.
	www.chem.ox.ac.uk /oc/sgdavies/presearch3.htm (1144 words)

	Aldol reaction Summary
		E and Z refer to the cis-trans stereochemical relationship between the enolate oxygen bearing the positive counterion and the highest priority group on the alpha carbon.
		If both the enolate and the aldehyde both contain pre-existing chirality, then the outcome of the "double stereodifferentiating" aldol reaction may be predicted using a merged stereochemical model that takes into account the enolate facial bias, enolate geometry, and aldehyde facial bias.
		In the syn-selective reactions, both enolization methods give the Z enolate, as expected; however, the stereochemical outcome of the reaction is controlled by the methyl stereocenter, rather than the chirality of the oxazolidinone.
	www.bookrags.com /Aldol_reaction (2537 words)

	Enolates and the Aldol Reactions
		Last time we worked through the reagents which oxidize aldehydes to carboxylic acids and the reagents which reduce aldehydes to primary alcohols and ketones to secondary alcohols.
		We also learned how enolate ions can be formed by the removal of an alpha hydrogen atom and how these enolate ions can act as nucleophiles toward bromine.
		Since that carbon already lost one hydrogen in forming the enolate intermediate essential to the aldol addition, it must have had two hydrogens in the original aldehyde.
	chemistry2.csudh.edu /rpendarvis/a-carbaldol.html (971 words)

	Carbon-Carbon Bonds from Esters
		Reduction of Esters, Grignard Reagents and Esters, Ester Enolates in Synthesis
		This is followed by attack of the nucleophilic alpha carbon of the enolate on the carbonyl carbon of a second molecule of the ester.
		When there are two ester groups on the same carbon chain (a diester), the enolate formed at the alpha carbon atom of one ester group can react with the carbonyl carbon of the other ester group.
	chemistry2.csudh.edu /rpendarvis/carb-enolate.html (986 words)

	Enolization
		of an enolate ion on a molecule of dibromine.
		This means that there is a very high concentration of the enolate ion in reaction 5, but not in reactions 3 and 4.
		This is a nucleophilic substitution reaction in which the enolate ion acts as a nucleophile and displaces a bromide ion from the dibromine.
	www.usm.maine.edu /~newton/Chy251_253/Lectures/Enolization/Enolization.html (1246 words)

	The Dispatch - Serving the Lexington, NC - News (Site not responding. Last check: )
		The Î±-carbon is important for enol and enolate based carbonyl chemistry as well.
		Chemical transformations effected by the conversion to either an enolate or enol generally lead to the Î±-carbon acting as a nucleophile becoming, for example, alkyated in the presence of primary haloalkane.
		An exception is in reaction with silyl- chlorides, -bromides, and -iodides, where the oxygen acts as the nucleophile to produce silyl enol ether.
	www.the-dispatch.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=alpha_carbon (503 words)

	Chapter 19, 21 Review
		All of these enolates have very similar structures, as can be seen by drawing resonsnce contributors or by examining the appropriate molecular orbitals.
		Selenenylation is useful because the phenyl selenide readily undergoes intramolecular elimanation to yield the conjugated enone.
		Enolate ions are in this category; their conjugate addition is called the Michael reaction.
	chemistry.umeche.maine.edu /CHY252/Ch22-Rev.html (543 words)

	Chemical Reactivity
		For example, aldehyde enolate bases are likely to undergo the aldol reaction during their formation, and ketones like 2-heptanone have two different alpha-carbons, each capable of enolization.
		The ambident nature of enolate anions also enables electrophilic attack at both oxygen and carbon, but in most synthesis applications bonding to carbon is desired.
		Finally, enolate anions may often be formed as E/Z stereoisomers, and it has been shown that reaction stereoselectivity, when new chiral centers are created, depends on the enolate configuration.
	www.cem.msu.edu /~reusch/VirtualText/special3.htm (9144 words)

	Free radical copper(II)-enolate polymerization initiators - Patent 5405913
		Because the solvent medium in which the oxidation reactions are performed is rendered basic by the coordinating agents for Cu.sup.II and/or the strong amine base, the enolate forms of the aldehydes and ketones are the intermediates that are oxidized.
		Since the negatively-charged enolate has a greater electron donating capability toward the Cu.sup.II ion than the non-enolized or enol form of an aldehyde or ketone, the presence of the enolate tends to preclude oxidation of the non-enolized or enol forms of aldehydes and ketones.
		Since equilibration of the Cu.sup.II -complexed enolate with the non-enolized form of the substrate within the coordination sphere of the Cu.sup.II ion appears to facilitate SET oxidation of the enolate, the rate of initiation can be increased by increasing the concentration of the substrate that is to be oxidized.
	www.freepatentsonline.com /5405913.html (8007 words)

	ARKAT USA, Inc.
		Polyfunctionalized pyrrole 6 is synthesized in the ring transformation of N-hydroxy-3,5-dinitro-4-pyridone 4 with enolate 2 derived from diethyl 3-oxogulutarate.
		Using triethylammonium enolate 2b is effective to improve the yield of 6 up to 30 % with easier experimental manipulations.
		The sodium enolate 2a was prepared from diethyl 3-oxoglutarate (1.09 mL, 6.0 mmol) and NaOEt (6.0 mmol) in EtOH (20 mL).
	www.arkat-usa.org /home.aspx?VIEW=MANUSCRIPT&MSID=535 (1181 words)

	EMPHASIS TOPICS FOR THE SECOND EXAM
		You should know that the enolate is the conjugate base of both the enol and the keto forms.
		In this reaction, both the enolate component and the carbonyl component are present in the same molecule.
		You should understand that the enolate of diethyl malonate or ethyl acetoacetate can be formed quantitatively using either hydroxide ion or an alkoxide ion, because the pKa of these beta dicarbonyl compounds is about 13.
	research.cm.utexas.edu /nbauld/teach/emphtopB2.html (3837 words)

	Oxidation and Reduction
		This is striking, because we are proposing that the alpha-hydrogen is acidic enough to be removed by a base no stronger than OH This is certainly not true of other C-H bonds, and it is only true here to the extent that the equilibrium constant for this step is very small.
		And, the resonance itself contributes to lowering the energy of the enolate, which makes it stable enough for a little of it to be formed at equilibrium.
		The alpha carbon in the enolate is all set up to behave as a nucleophile, providing a pair of electrons to make a new bond to a molecule of bromine.
	chemistry2.csudh.edu /rpendarvis/OxRed.html (1920 words)

	Rhodium(I) and Iridium(I) Complexes with -Keto Phosphine or Phosphino Enolate Ligands. Catalytic Transfer ...
		The cationic complex 20 and the phosphino enolate complexes 4, 7, and 16 catalyze the hydrogenation and the isomerization of 1-hexene.
		The rhodium phosphino enolate carbonyl complexes 7 and 13 are very active catalysts for transfer dehydrogenation of cyclooctane with norbornene under hydrogen pressure (7 MPa) at 60-90
		In the presence of 1 equiv of a triarylphosphine, rhodium phosphino enolate complexes not containing carbon monoxide, such as 22, proved to be active catalysts for transfer dehydrogenation at 70
	pubs.acs.org /cgi-bin/abstract.cgi/orgnd7/1996/15/i26/abs/om960814h.html (386 words)

	Reference.com/Encyclopedia/Enol
		Enols (and enolates) are important intermediates in many organic reactions.
		The words enol and alkenol are portmanteaux of the words alkene (or just -ene, the suffix given to alkenes) and alcohol (which represents the enol's hydroxyl group).
		Vitamin C is a sugar acid containg an enol bond.
	www.reference.com /browse/wiki/Enol (526 words)

	Enolate anion - Article from FactBug.org - the fast Wikipedia mirror site
		An enolate anion is an anion derived by loss of a proton from the alpha carbon of a carbonyl group; it is the anion of an enol.
		For instance, a base abstracts one proton from acetone to form enolate anion.
		The enolate anion is stabilised by resonance and therefore the alpha hydrogen is acidic.
	www.factbug.org /cgi-bin/a.cgi?a=498129 (102 words)

	Carbonyl Reactivity
		The base-catalyzed reaction proceeds via an enolate anion donor species, and the kinetically favored proton removal is from the less substituted alpha-carbon.
		Modestly electrophilic reactants such as alkyl halides are not sufficiently reactive to combine with neutral enol tautomers, but the increased nucleophilicity of the enolate anion conjugate base permits such reactions to take place.
		In this application one equivalent of diisopropylamine is produced along with the lithium enolate, but this normally does not interfere with the enolate reactions and is easily removed from the products by washing with aqueous acid.
	www.cem.msu.edu /~reusch/VirtualText/aldket2.htm (3430 words)

	Chapter 21: Claisen condensation
		The reaction involves an ester enolate reacting with another molecule of the ester.
		Try to recognise the two units that came together and identify the nucleophilic (enolate) portion and the electrophilic (carbonyl) portion.
		The nucleophilic ester enolate attacks the carbonyl C of another ester in a nucleophilic substitution process giving the tetrahedral intermediate.
	library.tedankara.k12.tr /carey/ch21-3-1.html (238 words)

	Tris(pyrazolyl)hydroborate Magnesium Alkyl Chemistry (Site not responding. Last check: )
		Reaction with halogens yields halides of the R group and the corresponding magnesium halide.
		The clean formation of the enolate complex is not expected on the basis of conventional Grignard reactions, where the alkoxide derivative {3-HB(3,5-R2)3}Mg{1-OC(CH3)3} would be the expected product.
		The stereochemistry of the tertiary alcohol has not yet been investigated, But it is very likely that the asymmetric environment of the ligand could induce enantioselectivity for the insertion.
	neon.chem.ox.ac.uk /ectoc-3/tpmgr.html (393 words)

	Chem 3020
		The enolate anion is the conjugate base of
		Enolate acts as nucleophile at the a carbon with Br-Br ® Br-C-C=O
		An enolate anion from a b-dicarbonyl compound serves as a nucleophile
	science.csustan.edu /cstessman/3020/ch22.htm (1225 words)

	List of Objectives for Chm223
		Draw enols and enolate anions of a given aldehyde or ketone.
		2) for the reaction of an enolate with an alkyl halide.
		Form ester enolates from the Bronsted-Lowry acid/base reaction of esters with lithium dialkylamides.
	www.wfu.edu /~welderco/223/223Fall06/223Fall06Objectives.htm (2722 words)

	enamine vs enolate
		Enolates can be made using NaOH, and they are a better nucleophile than enamines.
		Enolates are more nucleophilic than enamines, because enolate has formal negative charge and electronegativity of N is less than O. Enolates accept most electrophiles at carbon so very useful to make new carbon-carbon bonds.
		Metalloenamine (like an enolate, but with nitrogen), however, are better nucleophiles than enolates.
	www.chemicalforums.com /index.php?topic=6129.msg27194 (306 words)

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