Condensation & Alpha Substitution - Chp 22 Flashcards
What is the difference between enol and keto?
keto: C=O
enol: R=C-OH
Which form does the equilibrium of keto-enol tautomers favor more? Keto form or enol form? Why?
keto form because the C=O is much stronger than a C=C.
What 2 factors stabilize the enol of B-dicarbonyl compounds?
Conjugation and intramolecular hydrogen bonding.
What factor is especially stabilizing when a 6-membered enol ring is formed?
Intramolecular hydrogen bonding.
How are enolates formed?
When a base removes a proton on a carbon that is alpha to a carbonyl group.
Is the C–H bond on the alpha carbon is more acidic than most other sp3 hybridized C–H bonds? Explain?
Yes, because the resulting enolate is resonance stabilized.
Are enolates Nu or electrophiles?
Nucleophiles…react with many electrophiles.
Enolate is resonance stabilized, it has two __________: What are they?
reactive sites; the carbon and oxygen atoms that bear the negative charge.
A nucleophile with two reaction sites is called __________.
an ambident nucleophile
What factors increase the acidity of protons compared to other compounds?
How close it is to a carbonyl (closer increases acidity) and how many resonance structures.
Is a racemic mixture optically active?
No.
If a stereocenter is retained (R is still R), then is it optically active?
Yes.
-OH and Br2 (halogenation) reacting with a carbonyl does what?
Adds 2 bromines to (less hindered) alpha carbon of the carbonyl group.
Halogenation with an acid (ex. CH3CO2H and Br2) would form an _____ intermediate.
enol
Does enolate alkylation (ex. LDA, THF, -78C, CH3I) produce enantiomers or racemic products?
Yes
What is the difference between a kinetic and thermodynamic enolate?
Kinetic: double bond forms on the less hindered alpha carbon
Thermodynamic: double bond forms on the more hindered alpha carbon
Are the reagents for kinetic and thermodynamic enolates different? Give examples.
Yes
Kinetic: LDA, THF, -78C
Thermo: NaOCH2CH, CH3CH2OH
NaBH4 and CH3OH does what to a carbonyl group?
Changes it to an alcohol group.
What kind of ketones give a positive iodoform test?
Methyl ketones.
Which is more stable between thermodynamic and kinetic product? Which is faster?
Thermo is more stable while kinetic is faster.
In the iodoform reaction, a methyl ketone is converted to the ________ upon treatment with excess iodine and hydroxide
carboxylate
I2, KOH does what to a carbonyl group?
Changes it to a carboxylic acid group.
List the order of increasing pKa: ester, amide, nitrile, B-diketone, B-keto ester, aldehyde, ketone, 1,3-diester, 1,3-dinitrile
amide, nitrile, ester, ketone, aldehyde, 1,3-diester, 1,3-dintirile, B-keto ester, B-diketone
