Lecture 12. Mechanisms in Carbonyl Chemistry

Question 1

What do carbonyl compounds contain ?

Answer 1

C=O double bonds

Question 2

What is a sigma bond ?

Answer 2

Head on overlap if sp2 hybrid orbitals

Question 3

What is a pi bond ?

Answer 3

Side on overlap of p orbitals

Question 4

What does a double bond contain ?

Answer 4

A sigma and pi bond

Question 5

What are carbonyl groups susceptible to at carbon?

Answer 5

Nucleophilic attack

Question 6

What does a nucleophilic attack on a carbonyl result in ?

Answer 6

A tetrahedral intermediate

Question 7

What does the fate of the tetrahedral intermediate depend on ?

Answer 7

1. Nucleophile
2. Nature of carbonyl
3. Reaction conditions

Question 8

What way do aldehyde and ketone tetrahedral intermediates react ?

Answer 8

Tend not to react further

Question 9

What way do ester and thioester tetrahedral intermediates tend to react ?

Answer 9

Will react further

Question 10

What way do amides tetrahedral intermediates tend to react ?

Answer 10

Reluctant to react

Question 11

What are aldehydes and ketones easily reduced to ?

Answer 11

Alcohols

Question 12

What does nature use NADH for ?

Answer 12

A hydride source for reduction reactions

Question 13

What are simple aldehydes susceptible to ?

Answer 13

Nucleophilic attack by even fairly poor nucleophiles like water forming hydrates

Question 14

What does the extent of hydrate formation depend on ?

Answer 14

The structure of the carbonyl compound

Question 15

How do larger substituents effect hydrate formation ?

Answer 15

Less favorable

Question 16

What is hemiacetal ?

Answer 16

Very similar to hydrates, except the nucleophile is n alcohol rather than water

Question 17

What form do sugars generally exist as ?

Answer 17

Cyclic hemiacetyls

Question 18

How are hemiacetyls formed ?

Answer 18

Slowly. using either an acid or base to catalyse the reaction

Question 19

How do acid catalysis effect the carbonyl group ?

Answer 19

Makes it more electrophilic

Question 20

How does base catalysis effect the nucleophile ?

Answer 20

Makes it more nucleophilic

Question 21

What can happen if a carbonyl has a potential leaving group on it ?

Answer 21

The tetrahedral intermediate formed after nucleophilic attack can collapse back to a new carbonyl compound

Question 22

When are nucleophilic acyl substitution more successful ?

Answer 22

1. The intended leaving group is a better leaving group than the nucleophile
2. The electrophile is reactive enough

Question 23

What leads to the formation of imines ?

Answer 23

The reaction of aldehydes or ketones with primary amines, in which the carbonyl oxygen is lost completely

Question 24

What does imine formation often require ?

Answer 24

Acid catalysis