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Chapter 18
Enols, Enolates, & the Aldol Condensation
32
Organic Chemistry
Undergraduate 2
02/26/2015

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Term
enolate ions/enolates
Definition
the anions that result from a strong base removing an alpha hydrogen from an aldehyde or a ketone
Term
kinetic enolate
Definition
the enolate formed when the base removes a hydrogen from the less-hindered alpha carbon which usually results in generating the less stable anion
Term
At room temperature & in the presence of a proton source such as a slight excess of ketone starting material, equilibration of the kinetic with the more stable _____ enolate takes place
Definition
thermodynamic
Term
ambident
Definition
a species that can react at two different sites to give two different products; "two fanged"; comes from the Latin word "ambi" for "both" & "dens" for "tooth"
Term
alkylation
Definition
a reaction that attaches an alkyl group to a reactive carbon
Term
alkenol (enol)
Definition
the product of protonation of an enolate ion at the oxygen that creates an unsaturated alcohol
Term
tautomerize
Definition
when an enol (an unstable isomer of an aldehyde or ketone) rapidly converts into the carbonyl system
Term
enol & keto isomers
Definition
the isomers involved in tautomerization
Term
enolization
Definition
the conversion of the keto into the enol form; has very small equilibrium constants for ordinary aldehydes & ketones because only traces of enol are present
Term
Does treatment of a ketone with traces of acid or base in D2O solvent lead to the complete exchange of all the alpha hydrogens?
Definition
yes!
Term
Is the formation of enols/enolates reversible?
Definition
yes!
Term
3 step mechanism of the acid-catalyzed halogenation of a ketone
Definition
1. enolization (this is the r.d.s.)
2. halogen attack
3. deprotonation
Term
What is the result of base-catalyzed halogenation of a ketone?
Definition
the reaction continues until it completely halogenates the same alpha carbon, leaving unreacted starting material
Term
Why does alkylation of an enolate work best with only halomethanes or primary haloalkanes?
Definition
the enolate ion is a very strong base, therefore E2 elimination converting the haloalkane into an alkene becomes a significant process
Term
What is the ideal ketone for alkylation?
Definition
has only one alpha hydrogen
Term
Is alkylation of an enamine superior to alkylation of an enolate?
Definition
yes!
Term
Aldehyde reactions with NaOH, H2O, and low temperatures result in _____ formation
Definition
aldol (name comes from ALDehyde & alcohOL)
Term
Aldehyde reactions with NaOH, H2O, and heat result in _____ formation
Definition
aldol condensation
Term
3 step mechanism of aldol formation
Definition
1. enolate generation
2. nucleophile attack
3. protonation
Term
condensation
Definition
combining two molecules into one with the elimination of a molecule of water
Term
crossed aldol condensation
Definition
carrying out an aldol condensation between the enolate of one aldehyde & the carbonyl carbon of another
Term
When can you efficiently synthesize a single aldol product from the reaction of two different aldehydes?
Definition
when one of the aldehydes has no enolizable hydrogens
Term
Is it possible to carry out aldol condensations between two carbonyl groups located in the same molecule?
Definition
yes!
Term
intramolecular aldol condensation
Definition
carrying out aldol condensations between two carbonyl groups located in the same molecule; important in the synthesis of cyclic compounds (especially 5 and 6 membered rings)
Term
enone
Definition
alpha,beta-unsaturated carbonyl
Term
difunctional compounds
Definition
molecules with two functional groups
Term
conjugate addition
Definition
when several reagents add to the conjugated pi system in a 1,4-manner
Term
What does the end result of conjugate addition appear to be?
Definition
1,2-addition of Nu-H to the carbon-carbon double bond
Term
organocuprate
Definition
empirical formula R2CuLi; may be prepared by adding two equivalents of an organolithium reagent to one of copper iodide (CuI)
Term
Michael addition
Definition
the reaction in which enolate ions undergo conjugate additions to an alpha,beta-unsaturated aldehyde or ketone
Term
What is the Michael "acceptor" in a Michael reaction?
Definition
the beta-carbon of the unsaturated carbonyl compound
Term
Robinson annulation
Definition
the synthetic sequence of a Michael addition followed by an intramolecular aldol condensation
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