Carbonyl Chemistry

Question 1

What increases aldehyde/ ketone hydration

Answer 1

Low steric hindrance (aldehydes have less)
Electron withdrawing groups on an adjacent carbon
Ring strain (hydration reduces strain, sp2->sp3)

Question 2

What is a hemiacetal?

Answer 2

A molecule containing an alcohol and ether bond on the same carbon

Question 3

Reaction of ketone/ aldehyde with alcohol

Answer 3

Reversible formation of hemiacetal

Question 4

What can hydroxyaldehydes do to increase stability?

Answer 4

Intramolecular cyclisation to form cyclic hemiactals

Question 5

What is the mechanism for hemiactals formation from alcohols and aldehydes/ ketones

Answer 5

Question 6

What are mixed acetals?

Answer 6

Acetals where the O-R groups are different

Question 7

How can a full acetal be formed by the reaction of aldehydes/ ketones with alcohol?

Answer 7

Acid catalysis via hemiacetal intermediates

Question 8

Is acid catalysed acetal formation reversible?

Answer 8

Yes, H2O is lost in the process

Question 9

What is the intermediate in forming acetals from hemiacetals?

Answer 9

Oxonium ion (RC=(OR+)R)

Question 10

What is the mechanism for the formation of acetals by acid catalysis?

Answer 10

Question 12

What are spiroacetals?

Answer 12

Intramolecular acetals, bicyclic containing 5 or 6 membered rings

Question 13

What is the mechanism for spiroacetal formation?

Answer 13

Question 15

What is an imine?

Answer 15

A compound with a C=N bond, the nitrogen analogues of aldehydes and ketones

Question 16

How do you form an imine

Answer 16

React a primary amine with a carbonyl under acid catalysis

Question 17

What is the mechanism for imine production

Answer 17

Question 18

What intermediates are found in the production of imines?

Answer 18

Hemiaminal and iminium ion

Question 19

What is the ideal pH for imine formation?

Answer 19

4<pH<6
If pH is <4 the nucleophilic addition of amine is too slow.
If pH >6 the elimination of water is too slow

Question 21

What reaction conditions must be maintained to form imines?

Answer 21

4<pH<6
Removal of water as reaction progresses

Question 22

Why must water be removed when forming imines?

Answer 22

The reaction is reversible in the presence of water

Question 23

What process occurs via an imine or iminium ion formed in situ?

Answer 23

Reductive amination

Question 24

What can stabilise an imine?

Answer 24

A second electronegative atom attached to Nitrogen
Oximes
Hydrazones
Semicarbozones

Question 25

Why do electronegative heteroatoms on imine nitrogens increase stability?

Answer 25

Allows for resonance forms Lone pair donates electron density to nitrogen Decreases polarization of C=N bond Raises energy of LUMO Less susceptible to nucleophilic attack (including water hydrolysis)

Question 27

What are enamines?

Answer 27

Compounds with a C=C bond adjacent to a C-N bond

Question 28

How are enamines formed?

Answer 28

Reaction of secondary amines with enolisable α-hydrogen on an aldehyde or ketone

Question 29

What is the mechanism to form an enamine?

Answer 29

Question 30

What is the synthetic use of enamines?

Answer 30

Acts like an enolate, especially aldehyde enolate equivalents. More stable than enolates

Question 32

What is a cyanohydrin?

Answer 32

A compound with a cyano group and hydroxyl group on the same carbon

Question 33

What conditions are cyanohydrins formed under?

Answer 33

Acidic (NaCN/HCl) Basic conditions reverse the reaction