Chapter 7 - Aldehydes and Ketones II

Question 1

What are the carbons adjacent to the carbonyl carbon called?

Answer 1

The a-carbon; the hydrogens attached to the a-carbon are called a-hydrogens.

Question 2

What does a basic solution do to the a-hydrogens?

Answer 2

a-hydrogens (very acidic, but less in ketones) will easily deprotonate in a basic solution.

Question 3

What stabilizes/destabilizes organic anions?

Answer 3

Electron-withdrawing groups like oxygen stabilize organic ions.

Electron-donating groups like alkyl groups destabilize organic ions.

Question 4

How can the enolate resulting from deprotonation be stabilized?

Answer 4

By resonance with the carbonyl.

Question 5

What are two key strong bases?

Answer 5

Lithium diisopropyl amide (LDA) and Potassium hydride (KH).

Question 6

Why are ketones less reactive toward nucleophiles?

Answer 6

Because of steric hindrance and a-carbon destabilization.

Question 7

What is Michael Addition?

Answer 7

When an enolate attacks an a,B-unsaturated carbonyl compound (a molecule with a multiple bond between the a- and B-carbons next to a carbonyl) creating a bond.

Question 8

What are Tautomers?

Answer 8

Isomers that can be interconverted by moving a hydrogen and a double bond. The keto and enol forms are tautomers of each other (a-racemixture).

Question 9

What is an Enolate?

Answer 9

A deprotonated Enole. Enolates are good nucleophiles.

Question 10

What are Kinetic Enolates?

Answer 10

Kinetically controlled product is formed more rapidly but is less stable because of strictly hindered bases. (Double bond to less substituted carbon)

Question 11

What are Thermodynamic Enolates?

Answer 11

Thermodynamically controlled product is formed more slowly, but is more stable and features the double bond being formed with the more substituted a-carbon.

Question 12

When are kinetic products favored (kinetic enolates)?

Answer 12

When reactions are:

• rapid
• irreversible
• lower in temperature
• strong, sterically hindered bases

Question 13

When are thermodynamic products favored (thermodynamic enolates)?

Answer 13

When reactions are:

• slow
• reversible
• higher temperatures
• weak, smaller bases

Question 14

What is Adol Condensation?

Answer 14

When the aldehyde or ketone acts both as an electrophile (keto form) and a nucleophile (enol or enolate form), and the end result is the formation of a carbon-carbon bond.

Question 15

Why are Enolates more nucleophilic than Enols?

Answer 15

Enolates are negatively charged.

Question 16

What is an Aldol?

Answer 16

A molecule with both an aldehyde and an alcohol functional group.

Question 17

What happens in a condensation reaction?

Answer 17

Two molecules are joined with the loss of a small molecule (usually water via dehydration). This results in an a-B-unsaturated carbonyl.

Question 18

What happens in a Retro-Aldol Reaction?

Answer 18

Reverse of an aldol condensation; aqueous base is added and heat is applied.

A bond is broken between the a- and B-carbons of a carbonyl, forming two aldehydes, two ketones, or one aldehyde and one ketone.

Question 19

What happens when you treat an aldehyde or ketone with a strong base?

Answer 19

It becomes more nucleophilic and generates a carbanion.