Condensation & Alpha Substitution - Chp 22

Question 1

What is the difference between enol and keto?

Answer 1

keto: C=O
enol: R=C-OH

Question 2

Which form does the equilibrium of keto-enol tautomers favor more? Keto form or enol form? Why?

Answer 2

keto form because the C=O is much stronger than a C=C.

Question 3

What 2 factors stabilize the enol of B-dicarbonyl compounds?

Answer 3

Conjugation and intramolecular hydrogen bonding.

Question 4

What factor is especially stabilizing when a 6-membered enol ring is formed?

Answer 4

Intramolecular hydrogen bonding.

Question 5

How are enolates formed?

Answer 5

When a base removes a proton on a carbon that is alpha to a carbonyl group.

Question 6

Is the C–H bond on the alpha carbon is more acidic than most other sp3 hybridized C–H bonds? Explain?

Answer 6

Yes, because the resulting enolate is resonance stabilized.

Question 7

Are enolates Nu or electrophiles?

Answer 7

Nucleophiles…react with many electrophiles.

Question 8

Enolate is resonance stabilized, it has two __________: What are they?

Answer 8

reactive sites; the carbon and oxygen atoms that bear the negative charge.

Question 9

A nucleophile with two reaction sites is called __________.

Answer 9

an ambident nucleophile

Question 10

What factors increase the acidity of protons compared to other compounds?

Answer 10

How close it is to a carbonyl (closer increases acidity) and how many resonance structures.

Question 11

Is a racemic mixture optically active?

Answer 11

No.

Question 12

If a stereocenter is retained (R is still R), then is it optically active?

Answer 12

Yes.

Question 13

-OH and Br2 (halogenation) reacting with a carbonyl does what?

Answer 13

Adds 2 bromines to (less hindered) alpha carbon of the carbonyl group.

Question 14

Halogenation with an acid (ex. CH3CO2H and Br2) would form an _____ intermediate.

Answer 14

enol

Question 15

Does enolate alkylation (ex. LDA, THF, -78C, CH3I) produce enantiomers or racemic products?

Answer 15

Yes

Question 16

What is the difference between a kinetic and thermodynamic enolate?

Answer 16

Kinetic: double bond forms on the less hindered alpha carbon
Thermodynamic: double bond forms on the more hindered alpha carbon

Question 17

Are the reagents for kinetic and thermodynamic enolates different? Give examples.

Answer 17

Yes
Kinetic: LDA, THF, -78C
Thermo: NaOCH2CH, CH3CH2OH

Question 18

NaBH4 and CH3OH does what to a carbonyl group?

Answer 18

Changes it to an alcohol group.

Question 19

What kind of ketones give a positive iodoform test?

Answer 19

Methyl ketones.

Question 20

Which is more stable between thermodynamic and kinetic product? Which is faster?

Answer 20

Thermo is more stable while kinetic is faster.

Question 21

In the iodoform reaction, a methyl ketone is converted to the ________ upon treatment with excess iodine and hydroxide

Answer 21

carboxylate

Question 22

I2, KOH does what to a carbonyl group?

Answer 22

Changes it to a carboxylic acid group.

Question 23

List the order of increasing pKa: ester, amide, nitrile, B-diketone, B-keto ester, aldehyde, ketone, 1,3-diester, 1,3-dinitrile

Answer 23

amide, nitrile, ester, ketone, aldehyde, 1,3-diester, 1,3-dintirile, B-keto ester, B-diketone